elision n.

"a striking or cutting off," especially "the cutting off or suppression of a letter, sound, or syllable in speaking or writing," 1580s, from Latin elisionem (nominative elisio) "a striking out, a pressing out," in grammar, "the suppression of a vowel," noun of action from past-participle stem of elidere (see elide).

Properly, in prosody, "the vanishing or metrical ignoring of a vowel at the end of a word before a vowel (or an h) at the beginning of another" [Saintsbury, "Manual of English Prosody"], as in Shakespeare's

Do't, and thou hast the one half of my heart ;

Do't not, thou splitt'st thine own.

But commonly extended in sense to the crushing out of vowels within a word, as in "vi(o)let," "di(a)mond," "wat(e)ry," "splitt(e)st." A favorite, necessary, and hideous practice among the old poets.