early 15c., "relieve (pain); make mild or more tolerable; reduce in amount or degree," from Latin mitigatus, past participle of mitigare "soften, make tender, ripen, mellow, tame," figuratively, "make mild or gentle, pacify, soothe," ultimately from mitis "gentle, soft" + root of agere "to do, perform" (from PIE root *ag- "to drive, draw out or forth, move"). For mitis de Vaan suggests cognates in Sanskrit mayas- "refreshment, enjoyment," Lithuanian mielas "nice, sweet, dear," Welsh mwydion "soft parts," Old Irish min "soft," from a PIE *mehiti- "soft." Related: Mitigated; mitigating; mitigates.
"mitigating, soothing, alleviating," 1540s, from Latin mitigantem, present participle of mitigare (see mitigate). As a noun, "something that mitigates," by 1838.
late 14c., mitigacioun "alleviation or diminution of sorrow, pain, or anything harsh, painful, severe, etc." (mid-14c. in Anglo-French), from Latin mitigationem (nominative mitigatio) "a seething," noun of action from past-participle stem of mitigare (see mitigate).
Proto-Indo-European root meaning "to drive, draw out or forth, move."
It forms all or part of: act; action; active; actor; actual; actuary; actuate; agency; agenda; agent; agile; agitation; agony; ambagious; ambassador; ambiguous; anagogical; antagonize; apagoge; assay; Auriga; auto-da-fe; axiom; cache; castigate; coagulate; cogent; cogitation; counteract; demagogue; embassy; epact; essay; exact; exacta; examine; exigency; exiguous; fumigation; glucagon; hypnagogic; interact; intransigent; isagoge; litigate; litigation; mitigate; mystagogue; navigate; objurgate; pedagogue; plutogogue; prodigal; protagonist; purge; react; redact; retroactive; squat; strategy; synagogue; transact; transaction; variegate.
It is the hypothetical source of/evidence for its existence is provided by: Greek agein "to lead, guide, drive, carry off," agon "assembly, contest in the games," agōgos "leader," axios "worth, worthy, weighing as much;" Sanskrit ajati "drives," ajirah "moving, active;" Latin actus "a doing; a driving, impulse, a setting in motion; a part in a play;" agere "to set in motion, drive, drive forward," hence "to do, perform," agilis "nimble, quick;" Old Norse aka "to drive;" Middle Irish ag "battle."