mid-15c., "ample, profuse," from Old French frequent, or directly from Latin frequentem (nominative frequens) "often, regular, repeated; in great numbers, crowded, numerous, filled, full, populous," which is of uncertain origin. Watkins says probably from PIE *bhrekw- "to cram together," and compares Greek phrassein "to fence in," Latin farcire "to cram," But Beekes regards the connection to the Greek word as "quite uncertain." Meaning "common, usual" is from 1530s; that of "happening at short intervals, often recurring" is from c. 1600.
late 15c., "visit or associate with," from Old French frequenter "attend frequently; assemble, gather together," from Latin frequentare "visit regularly; do frequently, repeat; assemble in throngs," from frequentem (see frequent (adj.)). Meaning "visit often" is from 1550s. Related: Frequented; frequenter; frequenting.