late 15c., "of or pertaining to a mother or motherhood; characteristic of mothers," from Old French maternel (14c.), from Vulgar Latin *maternalis, from Latin māternus "maternal, of a mother," from māter "mother" (see mother (n.1)). From 1650s as "inherited or derived from a mother;" by 1784 as "motherly, having the instincts of a mother." Related: Maternally.

"a name derived from a mother or maternal ancestor," 1794, a hybrid from Latin māter "mother" (see mother (n.1)) + Greek-based ending from patronymic. As an adjective, "pertaining to or being derived from a mother or maternal ancestor," from 1874.

"of or pertaining to maternal rule or rule by females," 1780 (in reference to bee colonies); see matriarch + -al (1). Related: Matriarchally.

by 1841, "a name derived from the name of a mother or maternal ancestor;" by 1844 as an adjective, from Late Greek metrōnymikos "named for one's mother," from mētēr (genitive mētros) "mother" (see mother (n.1)) + onyma "name" (from PIE root *no-men- "name"). Related: Metronymically (1822).

"government by a mother or mothers; form of social organization in which the mother is the head of the family and the descendants are reckoned through the maternal side," formed in English 1881 from matriarch + -y (4) and "patterned after patriarchy" [Barnhart].

title of a military commander in Muslim north Africa, 1650s, from Turkish dai "maternal uncle," a friendly title used of older men, especially by the Janissaries of Algiers of their commanding officers. As these often became rulers in the colony it was used in English as the title of governor of Algiers under Ottoman rule, There were also deys in Tunis and Tripoli.

late 13c., from Old French oncle, from Latin avunculus "mother's brother" ("father's brother" was patruus), literally "little grandfather," diminutive of avus "grandfather," from PIE root *awo- "grandfather, adult male relative other than one's father" (source also of Armenian hav "grandfather," Hittite huhhas "grandfather," Lithuanian avynas "maternal uncle," Old Church Slavonic uji "uncle," Welsh ewythr "uncle"). Boutkan, however, says "the root probably denoted members of the family of the mother." 

Replaced Old English eam (usually maternal; paternal uncle was fædera), which represents the Germanic form of the same root (source also of Dutch oom "uncle, grandfather, brother-in-law," Old High German oheim "maternal uncle, son of a sister" German Ohm "uncle," Old Norse afi "grandfather").

Also from French are German, Danish, Swedish onkel. As a familiar title of address to an old man, attested by 1793; in the U.S. South, especially "a kindly title for a worthy old negro" [Century Dictionary]. First record of Dutch uncle (and his blunt, stern, benevolent advice) is from 1838; Welsh uncle (1747) was the male first cousin of one's parent. To say uncle as a sign of submission in a fight is North American, attested from 1909, of uncertain signification.

"of or pertaining to an uncle," 1789, from Latin avunculus "maternal uncle," diminutive of avus (see uncle) + -ar. Used humorously for "of a pawnbroker" (uncle was slang for "pawnbroker" from c. 1600 through 19c.).

Being in genteel society, we would not, of course, hint that any one of our readers can remember so very low and humiliating a thing as the first visit to "my Uncle"—the first pawnbroker. We have been assured though, by those whose necessities have sometimes compelled them to resort, for assistance, to their avuncular relation, that the first visit—the primary pawning—can never be forgotten. [Household Words, May 15, 1852]