mid-14c., "belonging to the male grammatical gender;" late 14c., "of men, of male sex," from Old French masculin "of the male sex" (12c.), from Latin masculinus "male, of masculine gender," from masculus "male, masculine; worthy of a man," diminutive of mas (genitive maris) "male person, male," a word of unknown origin. The diminutive form might be by pairing association with femininus (see feminine). Meaning "having the appropriate qualities of the male sex, physically or mentally: Manly, virile, powerful" is attested by 1620s. As a noun, "masculine gender," from c. 1500.
1928 (n.) "tough guy," from Spanish macho "male animal," noun use of adjective meaning "masculine, virile," from Latin masculus (see masculine). As an adjective, "ostensibly manly and virile," attested in English by 1959 (Norman Mailer).
"to make masculine, make manly or strong," 1620s, from Latin masculatus, from masculus (see masculine). Obsolete by late 19c. Related: Masculated; masculating. Also in same sense is masculinize (1912).
"to deprive of the male functions, deprive of virility or procreative power," c. 1600, from Latin emasculatus, past participle of emasculare "castrate," from assimilated form of ex "out, away" (see ex-) + masculus "male, manly" (see masculine). Originally and usually in a figurative sense in English. Related: Emasculated; emasculating.
early 14c., 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").
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.
Sense extended in Vulgar Latin from young humans to female of other animals, then to females generally. Compare Latin masculus, also a diminutive (see masculine). Spelling altered late 14c. in erroneous imitation of male. In modern use usually as an adjective (early 14c.). Reference to implements with sockets and corresponding parts is from 1660s.