(1):

(a.) Placed at the beginning; standing at the head, as of a list or series; as, the initial letters of a name.

(2):

(n.) The first letter of a word or a name.

(3):

(v. t.) To put an initial to; to mark with an initial of initials.

(4):

(a.) Of or pertaining to the beginning; marking the commencement; incipient; commencing; as, the initial symptoms of a disease.