Why is the ninth month called September?
c.1300, "an equal in rank or status" (early 13c. in Anglo-Latin), from Anglo-French peir, Old French per (10c.), from Latin par "equal" (see par (n.)). Sense of "a noble" (late 14c.) is from Charlemagne's Twelve Peers in the old romances, who, like the Arthurian knights of the Round Table, originally were so called because all were equal. Sociological sense of "one of the same age group or social set" is from 1944. Peer review attested by 1970. Peer pressure is first recorded 1971.
"to look closely," 1590s, variant of piren (late 14c.), with a long -i-, probably related to or from East Frisian piren "to look," of uncertain origin. Influenced in form and sense by Middle English peren (late 14c.), shortened form of aperen (see appear). Related: Peered; peering.