Real Dictionary

initial
Initials are the capital letters which begin each word of a name. For example, if your full name is Michael Dennis Stocks, your initials will be M. D.S.
You use initial to describe something that happens at the beginning of a process.

initial in American English
having to do with, indicating, or occurring at the beginning
adjective: of, pertaining to, or occurring at the beginning; first
noun: an initial letter, as of a word
transitive verb: to mark or sign with an initial or the initials of one's name, esp. as a token of preliminary or informal approval

initial in British English
adjective: of, at, or concerning the beginning
noun: the first letter of a word, esp a person's name
verb: to sign with one's initials, esp to indicate approval; endorse