 The term, from Latin, for the main upper arm flexor in the singular is the "biceps muscle" (from "biceps brachii"); however, many English speakers take it to be a plural and refer to the muscle of only one arm, by back-formation, as "a bicep".The correct—although very seldom used—Latin plural is "bicipites".The word "sastrugi" (hard ridges on deep snow) is of Russian origin and its singular is "sastruga"; but the imagined Latin-type singular "sastrugus" has sometimes been used.