It forms all or part of: ablution; alluvium; deluge; dilute; elution; lather; latrine; launder; lautitious; lavage; lavation; lavatory; lave; lavish; lotion; lye.
It is the hypothetical source of/evidence for its existence is provided by: Greek louein "to wash, bathe;" Latin lavare "to wash," luere "to wash;" Old Irish loathar "basin," Breton laouer "trough;" Old English leaþor "lather," læg "lye."
"moisten and rub (a bruised or injured part of the body) with a liquid substance," 1610s, from Medieval Latin embrocatus, past participle of embrocare, from Late Latin embrocha, from Greek embrokhe "lotion, fomentation," from embrekhein "to soak in, foment," from assimilated form of en (see en- (2)) + brekhein "to water, wet, rain, send rain," related to brokhe "rain," from PIE root *mergh- "to wet, sprinkle, rain." Related: Embrocated; embrocating; embrocation (early 15c.).
1540s, probably from Old English wice "Applied generally or vaguely to various trees having pliant branches" [OED], from wican "to bend" (from PIE root *weik- (2) "to bend, to wind") + hæsel, used for any bush of the pine family (see hazel (n.)). The North American bush, from which a soothing lotion is made, was so called from 1670s. This is the source of the verb witch in dowsing.