Definition of: capital letter

In writing and printing, the form of the alphabetic letter used at the beginning of a sentence, with proper names, etc.: in printing called cap or upper case letter as distinguished from lower case letter. Compare CASE² (def. 3).
—small capital A letter used in printing having the same form as but of smaller size than the CAPITAL of the same font: also called small cap. In this dictionary cross–references are in SMALL CAPITALS.