1. The first LETTER of a WORD, usually capitalized in a proper NAME: the L of London, the G, B, S of George Bernard Shaw. The practice of using initials or POINTS in handwriting and print has encouraged the growth of such ABBREVIATIONS as symbols, formulas, INITIALISMS, and ACRONYMS: for example, a stands, among others, for acre and are (units of land measurement); e.g. stands for LATIN exempli gratia for the sake of an example; BBC for British Broadcasting Corporation; NATO for North Atlantic Treaty Organization.
2. The large ornamental letter at the start of a page or chapter, especially in an illuminated manuscript.
in·i·tial / iˈnishəl/ • adj. existing or occurring at the beginning: our initial impression was favorable. ∎ (of a letter) at the beginning of a word. • n. (usu. initials) the first letter of a name or word, typically a person's name or a word forming part of a phrase: they carved their initials into the tree trunk. • v. (-tialed , -tial·ing ; Brit. -tialled, -tial·ling) [tr.] mark or sign (a document) with one's initials, esp. in order to authorize or validate it. ∎ agree to or ratify (a treaty or contract) by signing it.