1620s, "kindred, partaking of the same nature or natural characteristics," from assimilated form of Latin com "with, together" (see con-) + genialis "of birth," thus, "kindred" (from PIE root *gene- "give birth, beget," with derivatives referring to procreation and familial and tribal groups). Sense of "agreeable" is first recorded 1711 on the notion of "having natural affinity." Also compare congenital.
also postpartum, 1837, "occurring after the birth of a child," from Latin post partum "after birth," from post "after" (see post-) + accusative of partus "a bearing, a bringing forth," from partus, past participle of parire "to bring forth, bear, produce, create; bring about, accomplish" (from PIE root *pere- (1) "to produce, bring forth"). Phrase post-partum depression is attested by 1929.
c. 1200, "noble birth, high rank or condition," from Old French noblece "noble birth, splendor, magnificence" (Modern French noblesse), from Vulgar Latin *nobilitia, from Latin nobilis (see noble (adj.)). For the Old French suffix -esse, is from Latin -itia, added to adjectives to form nouns of quality, compare fortress.
Post-Middle English uses are perhaps reborrowings from French. The meaning "persons of noble rank" is from 1590s. The French phrase noblesse oblige "privilege entails responsibility, noble birth or rank compels noble acts" (literally "nobility obliges") is attested in English by 1837.
