n. 词首非重读短元音的脱落

[ noun ]
the gradual disappearance of an initial (usually unstressed) vowel or syllable as in `squire' for `esquire'
<noun.process>

Aphesis \Aph"e*sis\, n. [Gr. ? a letting go; ? + ? to let go.]
The loss of a short unaccented vowel at the beginning of a
word; -- the result of a phonetic process; as, squire for
esquire. --New Eng. Dict.