late 14c., basken "to wallow" (especially in warm water or blood, of unknown etymology. The Middle English Compendium rejects the derivation from Old Norse baðask "to bathe oneself" (with loss of middle syllable), reflexive of baða "bathe" (see bathe) + Proto-Germanic *-sik "one's self" (source also of German sich; see -sk).
Meaning "soak up a flood of warmth" is apparently due to Shakespeare's use of the word in reference to sunshine in "As You Like It" (1600). Related: Basked; basking.
1590s, "destroy the clarity of" (a transferred sense); literal sense ("to bathe in mud") is from c. 1600; perhaps frequentative formation from mud, or from Dutch moddelen "to make (water) muddy," from the same Proto-Germanic source. Sense of "to make muddy" is from 1670s; that of "make confused, bewilder" is recorded by 1680s. Meaning "to bungle" is from 1885. Related: Muddled; muddling.
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."
The modern noun might be a 16c. redevelopment from the verb. Meaning "violent perspiration" (especially of horses) is from 1650s; hence the transferred sense "state of agitation" (such as induces sweating), attested from 1839.
Intransitive use from 1590s. Meaning "to boil slowly, to cook meat by simmering it in liquid" is attested from early 15c. The meaning "to be left to the consequences of one's actions" is from 1650s, especially in figurative expression to stew in one's own juices. Related: Stewed; stewing. Slang stewed "drunk" first attested 1737.
c. 1200, scalden, "to be very hot;" also "to affect (someone) painfully by short exposure to hot liquid or steam," from Old North French escalder "to scald, to scorch" (Old French eschalder "heat, boil up, bubble," Modern French échauder), from Late Latin excaldare "bathe in hot water" (source also of Spanish escaldar, Italian scaldare "heat with hot water"), from Latin ex "out, out of" (see ex-) + calidus "hot" (from PIE root *kele- (1) "warm"). Related: Scalded; scalding.
"[T]he word entered at an early date into the Scandinavian languages" [OED]. The noun is c. 1600, from the verb, "burn or injury to the skin by hot liquid or steam."