algolagnia (n.)

word-forming element denoting "pain," from Greek algos "pain," algein "to feel pain," which is of unknown origin. Related to alegein "to care about," originally "to feel pain."

*slēg-, also *lēg-, Proto-Indo-European root meaning "be slack, be languid."

It forms all or part of: algolagnia; catalectic; laches; languid; languish; lax; lease; lessor; lush; relax; release; relish; slack (adj.); sleep.

It is the hypothetical source of/evidence for its existence is provided by: Greek legein "to leave off, stop," lagnein "to lust;" Latin languere "to be faint, weary," laxus "wide, spacious, roomy;" Old Church Slavonic slabu "lax, weak;" Lithuanian silpnas "weak."

also sadomasochism, "coexistence of sadism and masochism in the same person," 1916, from combining form of sadism + masochism. The abbreviation S & M is attested by 1965. An earlier word for sexualities that focused on violence (not quite the same thing) was algolagnia.