The Collaborative International Dictionary of English v.0.48:

Apheresis \A*pher"e*sis\ (?; 277), n. [L. aphaeresis, Gr. ?, fr.
   ? to take away; ? + ? to take.]
   1. (Gram.) The dropping of a letter or syllable from the
      beginning of a word; e. g., cute for acute.
      [1913 Webster]

   2. (Surg.) An operation by which any part is separated from
      the rest. [Obs.] --Dunglison.
      [1913 Webster]

WordNet (r) 3.0 (2006):

apheresis
    n 1: (linguistics) omission at the beginning of a word as in
         `coon' for `raccoon' or `till' for `until' [syn:
         aphaeresis, apheresis]
    2: a procedure in which blood is drawn and separated into its
       components by dialysis; some are retained and the rest are
       returned to the donor by transfusion [syn: apheresis,
       pheresis]