aphesis

aphesis \AF-uh-sis\, noun:

Historical Linguistics. the disappearance or loss of an unstressed initial vowel or syllable, as in the formation of the word slant fromaslant.

In particular, phrases forming a solid continuous unit and having only one main stress can become subjected to aphesis and other phonetic changes.
-- Mikko Luukko, Grammatical Variation in Neo-Assyrian, 2004

In other cases we witness aphaeresis, or rather aphesis, the loss of initial segments in the MAGY words…
-- György Busztin, The Legacy of the Barang People, 2006

Aphesis is derived from the Greek word of the same spelling meaning "a letting go."