washer (n.2)
"flat ring for sealing joints or holding nuts," mid-14c., generally considered an agent noun of wash (v.), but the sense connection is difficult, and the noun may derive instead from the ancestor of French vis "screw, vise" (see vise).
washer (n.1)
1520s, "person who washes," agent noun from wash (v.). From 1808 as "machine that washes." Washer-woman is from 1630s; earlier wash-woman (1580s).