Biceps comes from the Latin words bis (twice) and caput (head). The biceps brachii is a muscle with two "heads" (or origins).

Biceps is both singular and plural, although about a quarter the usage on the Internet is in the pseudo-singular form of "bicep". (To be strictly correct, the plural of biceps is bicipites, used only by those who wish to flaunt their learning to the of point annoyance).

The biceps brachii was named in 1734 by the German anatomist Bernhard Weiss (who went by the Latinized name of Albinus).

Albinus (1697-1770)
clendening.kumc.edu