Aphesis

In phonetics, aphaeresis /əˈfɪəɹəsɪs/ (Greek apo away, hairein to take) is the loss of one or more sounds from the beginning of a word; especially, the loss of an unstressed vowel.

Aphaeresis or aphesis as a historical sound change
In historical phonetics, the term "aphaeresis" is often but not always limited to the loss of an unstressed vowel. (The OED gives this particular kind of aphaeresis the name aphesis /ʼæfɪsɪs/.)

The loss of any sound

 * English [k]nife pronounced ['naɪf]
 * German [St]rand > Finnish ranta "beach"

The loss of an unstressed vowel

 * Greek episkopos > Vulgar Latin [e]biscopu > English bishop
 * English [a]cute > cute
 * English [E]gyptian > Gyptian > Gypsy
 * English [a]mend > mend
 * English [e]scape + goat > scapegoat
 * Old French evaniss- > English vanish
 * English esquire > squire

Aphaeresis as a poetic device

 * English it is > poetic 'tis

Aphaeresis in informal speech

 * Spanish está > Rioplatense Spanish [e]tá > ta ("is")
 * Norwegian [automo]bil > bil "car"