Origin and history of fem

early 14c., female, femele, "woman, human being of the sex which brings forth young," from Old French femelle "woman, female" (12c.), from Medieval Latin femella "a female," from Latin femella "young female, girl," diminutive of femina "woman, a female" ("woman, female," literally "she who suckles," from PIE root *dhe(i)- "to suck").

The sense in Vulgar Latin was extended from young humans to female of other animals, then to females generally. Compare Latin masculus, also a diminutive (see masculine). The spelling femele is etymological but in Middle English the word was altered in erroneous imitation of unrelated male.

In modern use usually an adjective (in which use it is attested from early 14c.). In reference to implements with sockets and corresponding parts from 1660s.

WHEN the Himalayan peasant meets the he-bear in his pride,

He shouts to scare the monster, who will often turn aside.

But the she-bear thus accosted rends the peasant tooth and nail.

For the female of the species is more deadly than the male.

[Kipling]