initial

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Of, relating to, or occurring at the beginning; first.
• adjective Designating the first letter or letters of a word.
• noun The first letter of a proper name.
• noun The first letter of each word of a person's full name considered as a unit.
• noun The first letter of a word.
• noun A large, often highly decorated letter set at the beginning of a chapter, verse, or paragraph.
• transitive verb To mark or sign with initials, especially for purposes of authorization or approval.

from The Century Dictionary.

• To put one's initial or initials to or on; sign or mark with initials: as, an initialed handkerchief; initialed paper.
• Of or pertaining to the beginning; incipient: as, the initial step in a proceeding.
• Placed at the beginning; standing at the head: as, the initial letter of a word, or of a chapter in a book.
• noun The initial or first letter of a word; an initial letter.
• noun The first letter of a book or writing, or of any division of it, distinguished from the body of the text by larger size or more ornamental character, or both.
• noun In plain-song, a tone with which a melody may begin. In strict usage the initials for each mode are prescribed, and called absolute initials.
• noun In steam-engines, an abbreviation of initial pressure (which see).

from the GNU version of the Collaborative International Dictionary of English.

• noun The first letter of a word or a name.
• transitive verb rare To put an initial to; to mark with an initial of initials.
• adjective Of or pertaining to the beginning; marking the commencement; incipient; commencing.
• adjective Placed at the beginning; standing at the head, as of a list or series.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Chronologically first, early; of or pertaining to the beginning, cause or origin
• adjective Spatially first, placed at the beginning, in the first position; especially said of the first letter of a word
• noun The first letter of a word or a name.
• noun In plural, the first letter of each word of a person's full name considered as a unit
• noun typography, calligraphy A distinguished initial letter of a chapter or section of a document.
• noun phonology onset, part of a syllable that precedes the syllable nucleus in phonetics and phonology.
• verb transitive To sign one's initial(s), as an abbreviated signature.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective occurring at the beginning
• verb mark with one's initials
• noun the first letter of a word (especially a person's name)