Words are mutable things, subject to constant tugs and tweaks in the everyday trade of conversation. Some drift far enough to become visibly different when written down. There are patterns to these drifts, for example aphaeresis, whereby a word loses its initial sound or sounds (’twas, ’cause, knock, ticket). Sounds are also lost from the ends of words by a process called apocope /ə’pɒkəpɪ/ – literally ‘cutting off’, from the Greek apokopē.
Apocope stands out when we see writing from older stages of the language, when it was more heavily inflected. Middle English singen led to modern sing, while Old English ridan gave us ride. The verb help was helpan in Old English and helpen in Middle English, and though its related past participle holpen survives in some US dialects, the word has otherwise definitively lost that final sound.
Silent letters at the end of a word are another indication that apocope has taken place: the ‘b’ in lamb and dumb, and the ‘n’ in damn, hymn and autumn, are all silent in Modern English but serve to remind us they were not always so ghostly.
Apocope is a term in diachronic (or historical) linguistics, as in the examples above. But it also applies on a shorter timescale to changes that are a sort of elision. Thus cinematograph gives us cinema; moving picture, movie; popular, pop; traditional, trad; veteran and veterinary surgeon, vet; microphone, mike; detoxification, detox; disrespect, dis or diss, and so on. School and college subjects are also shortened this way: math(s), psych, chem.
It happens to the most familiar phrases. Saying cup of tea in informal company, we tend to forgo precise pronunciation of the middle word, sounding /əv/ simply as /ə/ to produce something more like ‘cup o’ tea’. Commonly spelt cuppa tea, this abbreviates further to cuppa. The loss of the /v/ sound is apocope. And receives similar treatment: the casual delivery of demotic speech means we are sometimes prone to omit the /d/ sound, so eventually it can disappear altogether from certain set phrases such as rock ’n’ roll and fish ’n’ chips.
While this process is underway, the resulting forms may remain somewhat colloquial, as with cred for credibility (as in street cred), fab for fabulous, and the recently discussed amaze for amazing. Through the slow rub of use in speech or the more immediate incentive of economy, the final sounds of many words were clipped without fuss or eroded gradually over time.

Stan:
Apocope will always please
The folks who think in headline-ese.
Stan: Re your point in the third paragraph. In words like damn, the final ‘n’ is of course not always silent – damnation, hymnal, autumnal etc. Whereas the final ‘b’ tends to remain silent, e.g in ‘lambing’, ‘dumbing-down’. But then there’s ‘dumbo’ – which Macmillan defines as ‘a stupid person’ (there’s a need for some pragmatic information here…)
Marc: Very good! And letters lost from days of old / Make room for more in sixty point bold.
Gill: That’s very true. I skated over that point a bit, and am glad to have it clarified in the comments.
I believe that the word fan is short for fanatic. I was amused to see the fans of the Australian tennis player Lleyton Hewitt calling themselves the “Fanatics”, probably unaware that they’d reverted to the earlier form of the word.
The b in climb, comb, dumb, lamb, tomb, jamb, womb is indeed apocope, but the final bs in crumb, numb, thumb have never been pronounced; they were added by analogy. Limb ‘arm, leg’ got its b by analogy with the less common limb ‘edge’.
Gerry: Interesting; I didn’t know Lleyton Hewitt’s fans called themselves fanatics. I imagine that use of the word makes it less pejorative for some people. The connection with fan is more explicit in Tony Scott’s film The Fan, in which Robert de Niro plays a fanatical fan of a baseball team.
John: Thanks for clarifying the status of other members of the –mb set. I wasn’t aware so many had gained the ‘b’ through analogy.
[…] “My fortnightly column at Macmillan Dictionary Blog continues with three new posts. First: Apocope is not to be dissed resumes an unofficial series on different types of word formation. Apocope involves the loss of […]