Of, relating to, or occurring at the beginning; first: took the initial step toward peace. Designating the first letter or letters of a word. The first letter of a proper name. The first letter of each word of a person's full name considered as a unit: stationery monogrammed with her initials. The first letter of a word. A large, often highly decorated letter set at the beginning of a chapter, verse, or paragraph. To mark or sign with initials, especially for purposes of authorization or approval.