ablution (n.)
Origin and meaning of ablution

"ritual washing," late 14c., from Latin ablutionem (nominative ablutio) "a washing, cleansing," noun of action from past-participle stem of abluere "to wash off, wash away, cleanse by washing," from ab "off, away from" (see ab-) + luere "to wash," from PIE root *leue- "to wash."

Related entries & more 
*leuə-, Proto-Indo-European root meaning "to wash."

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."
Related entries & more 
baptism (n.)
"initiatory sacrament of the Christian faith, consisting in immersion in or application of water by an authorized administrator," c. 1300, bapteme, from Old French batesme, bapteme "baptism" (11c., Modern French baptême), from Latin baptismus, from Greek baptismos, noun of action from baptizein (see baptize). The -s- was restored in late 14c.

The signification, qualifications, and methods of administration have been much debated. Figurative sense "any ceremonial ablution as a sign of purification, dedication, etc." is from late 14c. Old English used fulluht in this sense (John the Baptist was Iohannes se Fulluhtere).

Phrase baptism of fire "a soldier's first experience of battle" (1857) translates French baptême de feu; the phrase originally was ecclesiastical Greek baptisma pyros and meant "the grace of the Holy Spirit as imparted through baptism;" later it was used of martyrdom, especially by burning.
Related entries & more