initial
n. countablen. the first letter of a name. You often use your initials to sign a document quickly.
n. the first letter of a person's name, especially when used as a shorthand signature. Often used in the plural to refer to the set of first letters of a full name.
Please write your initials at the bottom of each page.
The artist signed the corner of the painting with her initials instead of her full name.
Legal contracts often require the signatory to place their initials on every page to ensure that no unauthorized substitutions have been made to the document's interior clauses.
From Middle French initial or directly from its Latin etymon initiālis (“of the beginning, incipient, initial”), from initium (“a going in, entrance, beginning”), from inire (“to go in, enter upon, begin”), from in (“in”) + ire (“to go”).
Commonly used in the plural ('initials') when referring to the first letters of both a given name and a surname.