also also-relievo, 1717, from Italian, literally "high-relief" in sculpture, from alto "high," from Latin altus (see alti-) + rilievo, from rilevare "to raise," from Latin relevare "to raise, lighten" (see relieve).
late 14c., releven, "alleviate (pain, etc.) wholly or partly, mitigate; afford comfort; allow respite; diminish the pressure of," also "give alms to, provide for;" also figuratively, "take heart, cheer up;" from Old French relever "to raise, relieve" (11c.) and directly from Latin relevare "to raise, alleviate, lift up, free from a burden," from re-, here perhaps an intensive prefix (see re-), + levare "to lift up, lighten," from levis "not heavy" (from PIE root *legwh- "not heavy, having little weight").
The notion is "to raise (someone) out of trouble." From c. 1400 as "advance to the rescue in battle, bring help to a besieged place;" also "return from battle; recall (troops)." Meaning "release from duty" is from early 15c. Related: relieved; relieving.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit laghuh "quick, small;" Greek elakhys "small," elaphros "light;" Latin levare "to raise," levis "light in weight, not heavy;" Old Church Slavonic liguku, Russian lëgkij, Polish lekki, Lithuanian lengvas "light in weight;" Old Irish lu "small," laigiu "smaller, worse;" Gothic leihts, Old English leoht "not heavy, light in weight."