I recently read a scene in a glowfic thread in which a wife, speaking to her husband, uses “fuck” where I would use “make love to.” While the primary meaning of both locutions is “copulate with,” they have very different connotations. “Fuck” has the secondary meaning of “injure, destroy, harm.” The sexual meaning, perhaps as a result, is closer to “rape” than “make love to.”1
The point in that scene may be that the wife has grown up in a very unpleasant society2 and had her attitude to sex distorted as a result. An alternative, I think more interesting, explanation is that the word has been so overused as to have lost, for many, its emotive effect. In other contexts I frequently see it used, sometimes as its present participle, to express a vaguely negative emotion with no sexual content at all, something I cannot imagine doing in my own speech. As one person put it online, “some people use ‘fuck’ as a comma.”
“Geek” is another example. The original meaning was a fool or freak, in 19th century America a performer in a geek show in a circus.3 By early in the 21st century the primary meaning had shifted to someone obsessively interested in a technical field, presumably on the theory that that was freaky. Since then most of the pejorative connotation has been lost, replaced in some contexts by the positive connotation of technical expertise. Nerd has similarly gone from an always negative term for someone overly intellectual and socially awkward to a sometimes positive term for someone very knowledgeable and passionate about a specific area.
The original meaning of “Hacker” was someone who did something in a cleverly non-standard way, the sort of software that worked brilliantly until the next time the operating system was updated and then did not work at all. I like to imagine a programmer observing for the first time an elephant’s solution to the problem of picking something up without hands: “What a hack.”
Over time the meaning shifted to someone who used programming skills to break into computers, probably because that is what “hacking” sounded as though it should mean to someone who did not know what it did mean. Over more time it lost some of the negative implication, was sometimes used to mean someone skilled with hardware or software, bringing it back to something closer to but less specific than its original meaning.
“Gay” has gone through two shifts of meaning in my lifetime. Its primary meaning when I was growing up was “cheerful” but it was acquiring the secondary meaning, by now primary, of male homosexual. Listening to chat on a World of Warcraft server ten or fifteen years ago I discovered that it had a new secondary meaning unconnected to either of the other two, an expression of mild disapproval: “That’s so gay.” The negative attitude to homosexuality had survived the loss of the meaning of the word.
Words used as pejoratives in a political context such as “fascist,” “racist,” and “Nazi” become less effective over time due to overuse; currently all three most often mean “someone some of whose views I disapprove, probably to my political right.” It would be interesting to know if in some circles it has by now lost both primary meaning and negative affect, become a self-identifier for groups, perhaps Trump supporters, commonly so labeled by their opponents: We Nazis. That would correspond to what happened to “Tory” some centuries ago.
From the 1500s to 1600s, the term Tory first emerged to refer to the Irish who were dispossessed of their lands and took to the woods, forming themselves into bands that subsisted on wild animals and goods taken from settlers. After these activities were suppressed, the term lost its original signification with English-speakers and was used to describe "an outlaw papist" or a "robber that is noted for outrages and cruelty". (Wikipedia)
By the late 17th century “Tory” had become the label of a British political party, a meaning which it has retained ever since. “Whig” had a similar, if less extreme, shift.
Yankee is another example, originally a derogatory term used by the British for American colonists it became a term of national pride for Americans, at least in the Northern states.
Something similar has happened to pejoratives applied to the left such as “red,” or “commie.” “Socialist” has, for a very long time, been used by the right as a negative term, by much of the left as a positive. By the time Bernie Sanders, a self-identified socialist, was competing for the Democratic nomination the negative usage had lost much of its force. Earlier still, in the European context, the meaning of “socialism” largely shifted from state socialism to welfare capitalism, most obviously in the Scandinavian welfare states. If I describe the American public school system as a socialist institution that will be interpreted by almost anyone, with the possible exception of a fellow economist, as a right wing complaint against what is taught, not as the observation, obviously true, that it is a means of production owned and controlled by a government.
The loss of a word’s negative connotation can be due, as in the example I started with, to overuse but it can also be due to a deliberate policy by the targeted group. An example would be “queer” used for homosexuals. While some still see it as a negative term others use it for deliberate self-identification.
“Bloody” is an interesting case. Its origin is disputed, with multiple theories, but it was used as a mild intensifier from at least 1670 to the early 18th century:
After about 1750 the word assumed more profane connotations. Johnson (1755) already calls it "very vulgar", and the original Oxford English Dictionary article of 1888 comments the word is "now constantly in the mouths of the lowest classes, but by respectable people considered 'a horrid word', on a par with obscene or profane language"
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Public use continued to be seen as controversial until the 1960s, but the word has since become a comparatively mild expletive or intensifier (Wikipedia)
Wikipedia has an interesting article on the word, including some entertaining false etymologies. The actual origin, in particular whether it initially combined the sexual and aggressive elements, is unclear.
Cheliax ruled by Asmodeus, the god of Hell, for anyone familiar with either the Pathfinder or the Glowfic version of the setting.
The 1975 edition of the American Heritage Dictionary, published a decade before the Digital Revolution, gave only one definition: "Geek [noun, slang]. A carnival performer whose act usually consists of biting the head off a live chicken or snake." (Wikipedia)
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There certainly is that process, and not only in English; the French foutre, originally meaning "fuck" (and derived from Latin futuo, which means the same thing), has now come to mean simply "do."
At the same time, there's a process in which words originally intended to be neutral and descriptive become abusive epithets. The words "moron," "imbecile," and "idiot" supposedly used to indicate different degrees of cognitive subnormality; certainly by the time I was in high school they had become insults (and there were also "moron" jokes), and the professional terms were educable, trainable, and custodial mental retardation; but then "retarded" and "retard" and "MR" became abusive epithets, and the conditions apparently are now called "intellectual disability." I expect that if "ID" becomes a term of abuse we will see yet another neologism.
Consider, too, the adoption of metaphorical expressions, as when the slightly learned word "pregnant," in the sense of "having numerous implications" ("a pregnant utterance"), was adopted to mean "with child" or "gravid," and then came to mean that primarily, and so strongly that people looked for less blunt expressions, such as "expectant."
Words seem to take on emotional overtones from the way people tend to regard the things those words refer to, regardless of how people intend them to be used.
A pair of words that have not so much changed their meanings but get substituted for one another according to the lay of the land is "progressive" and "liberal". I'm not so sure of the initial replacement of "progressive" with "liberal", likely at the beginning of the New Deal, but it must have been that "progressive" was becoming less popular, so they stole our word. I'm on firmer ground with the recent reversion, eschewing "liberal" and substituting "progressive". That was completely conscious and intentional, because "liberal" had become malodorous to much of the population.