aphaeresis
noun
aphaer·e·sis ə-ˈfer-ə-səs 
plural aphaereses ə-ˈfer-ə-ˌsēz
: the loss of one or more sounds or letters at the beginning of a word (as in round for around and coon for raccoon)
aphaeretic
ˌa-fə-ˈre-tik
adjective 
Word History
Etymology
borrowed from Late Latin, borrowed from Greek aphaíresis "taking away, removal, dropping of a letter or sound from the beginning of a word," from aphaire-, stem of aphairéō, aphaireîn "to take away" (from aph-, assimilated variant of apo- apo- + hairéō, haireîn "to take, grasp," of obscure origin) + -sis -sis
First Known Use
circa 1550, in the meaning defined above