Origin: 1350–1400; Middle English relaxen < Latin relaxāre to stretch out again, loosen, equivalent to re-re- + laxāre to loosen, derivative of laxus slack, lax
c.1420, "to make (something) less compact or dense," from O.Fr. relaxer (14c.), from L. relaxare "relax, loosen, open," from re- "back" + laxare "loosen," from laxus "loose" (see lax). Of persons, attested from 1837, "to become less formal;" meaning "to become less tense" is