Pronunciation: (u-fer'u-sis for 1; af"u-rē'sis for 2),[key] —n. 1. Also,aphaeresis.the loss or omission of one or more letters or sounds at the beginning of a word, as in squire for esquire, or count for account. 2. Med.the withdrawal of whole blood from the body, separation of one or more components, and return by transfusion of remaining blood to the donor.