late 14c., relaxacioun, "a rupture, a hernia" (a sense now obsolete); mid-15c., "remission of a burden or penalty," from Old French relaxacion (14c.) and directly from Latin relaxationem (nominative relaxatio) "an easing, mitigation, relaxation," noun of action from past-participle stem of relaxare "loosen, open, stretch out" (see relax).
Meaning "relief from hard work or ordinary cares; a state or occupation intended to give mental or bodily relief after effort or ordinary occupations and cares" is from 1540s. Sense of "remission or abatement of rigor or intensity" is from 1690s.
"violent muscular spasms, rapidly alternating contraction and relaxation of a muscle," 1817, from Modern Latin, from Greek klonos "turmoil, any violent motion; confusion, tumult, press of battle," a word of uncertain origin. Related: Clonicity.
1771, "causing or distinguished by relaxation," from Latin relaxantem (nominative relaxans), present participle of relaxare "to loosen, stretch out" (see relax). As a noun, "a medicine or treatment that relaxes or opens," from 1832. An earlier adjective was relaxative "having the quality of relaxing" (1610s).
"normal rhythmic relaxation of the heart" (alternating with the systole), 1570s, from medical Latin diastole, from Greek diastole "drawing asunder, dilation," from diastellein, from dia "through; thoroughly, entirely" (see dia-) + stellein "to set in order, arrange, array, equip, make ready," from PIE *stel-yo-, suffixed form of root *stel- "to put, stand, put in order," with derivatives referring to a standing object or place. Related: Diastolic.
c. 1200, remissioun, "forgiveness or pardon (of sins)," from Old French remission "forgiveness (of sins), relief" (12c.) and directly from Latin remissionem (nominative remissio) "relaxation, diminishing," etymologically "a sending back, sending away," noun of action from past-participle stem of remittere "slacken, let go, abate" (see remit).
From late 14c. as "release from duty or obligation." Of diseases, fevers, "abatement, temporary subsidence," from early 15c. General sense of "diminution of force or effects" is from c. 1600. By 1736 as "abatement of penalty or punishment."