Source : Webster's Revised Unabridged Dictionary (1913)

Initial \In*i"tial\, a. [L. initialis, from initium a going in,
   entrance, beginning, fr. inire to go into, to enter, begin;
   pref. in- in + ire to go: cf. F. initial. See {Issue}, and
   cf. {Commence}.]
   1. Of or pertaining to the beginning; marking the
      commencement; incipient; commencing; as, the initial
      symptoms of a disease.

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

Initial \In*i"tial\, n.
   The first letter of a word or a name.

Initial \In*i"tial\, v. t. [imp. & p. p. {Initialed}; p. pr. &
   vb. n. {Initialing}.]
   To put an initial to; to mark with an initial of initials.
   [R.]

Source : WordNet®

initial
     adj : occurring at the beginning; "took the initial step toward
           reconciliation"
     [also: {initialling}, {initialled}]

initial
     v : mark with one's initials
     [also: {initialling}, {initialled}]

initial
     n : the first letter of a word (especially a person's name); "he
         refused to put the initials FRS after his name"
     [also: {initialling}, {initialled}]