Can't vs cannot

[Smiley]

What is the word for the (don't, couldn't, wouldn't won't)? as in, instead of cannot, do not, will not, would not?   I know it's not slang... maybe shortened words? It's really annoying me!

[kempie]

Verbal contraction

[LordyGeordie]

abbreviation

[Hgrove]

Could it be elision?

[silly moo]

You're right Hgrove
Following taken from on-lone phronology course
Elision refers to when a sound or syllable is lost or omitted. It particularly affects: consonant clusters; weakly stressed syllables that are not especially missed; and words that end in an alveolar consonant and that are immediately followed by a word beginning with a consonant. The sounds that are elided are those sounds that are so weakly articulated that they no longer have any auditory significance.
Some elided syllables are represented in standard punctuation, for example, /I'm/ should be /I am/. In standard speech, the missing vowel is understood and so meaning does not suffer from this contraction.
Elision is one of the reasons for the great mismatches found in English between a word's spelling and its pronunciation. /wednesday/, for example, was originally a contraction of /Odin's day/ while today, Odin is barely discernable as the /d/ is no longer pronounced.
Elision is most commonly used in, but is not exclusive to, connected speech. The faster the speech, the more likely that sounds and syllables will be elided.

[bernardo]

I think it might be clitic or enclitic or proclitic or something, but I can't be bothered to google first to check before answering.

[marmaduke]

It's a contraction

[jno]

Elision is the general word for sounds that get missed out. But contraction might be a better term for the particular words - auxiliary verbs - you list. The difference would be that elisions are permanent, and only happen in spoken language, not written language (people may say Wensday but the spelling is still Wednesday). Contractions on the other hand exist alongside the uncontracted form - cannot as well as can't are both good English - and have their own spellings.

[Earthlady]

Have to agree with jno

[U.S. Amy]

Contraction

[marmaduke]

Which is what I said, and very pithily too.