Aphesis is the loss of an unstressed sound or syllable at the beginning of a word. In poetry, it appears in shortened forms such as neath for beneath or mid for amid, often to fit meter, rhythm, or a more compact poetic style.
Example
I stood neath the pine at dusk
and heard the river call me home.
Related Definitions
[n] the gradual disappearance of an initial (usually unstressed) vowel or syllable as in `squire' for `esquire'