lessor n.

*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."

English agent noun ending, corresponding to Latin -or. In native words it represents Old English -ere (Old Northumbrian also -are) "man who has to do with," from Proto-Germanic *-ari (cognates: German -er, Swedish -are, Danish -ere), from Proto-Germanic *-arjoz. Some believe this root is identical with, and perhaps a borrowing of, Latin -arius (see -ary).

Generally used with native Germanic words. In words of Latin origin, verbs derived from past participle stems of Latin ones (including most verbs in -ate) usually take the Latin ending -or, as do Latin verbs that passed through French (such as governor); but there are many exceptions (eraser, laborer, promoter, deserter; sailor, bachelor), some of which were conformed from Latin to English in late Middle English.

The use of -or and -ee in legal language (such as lessor/lessee) to distinguish actors and recipients of action has given the -or ending a tinge of professionalism, and this makes it useful in doubling words that have a professional and a non-professional sense (such as advisor/adviser, conductor/conducter, incubator/incubater, elevator/elevater).

late 15c., "to take a lease," from Anglo-French lesser (13c.), Old French laissier "to let, let go, let out, leave" "to let, allow, permit; bequeath, leave," from Latin laxare "loosen, open, make wide," from laxus "loose" (from PIE root *sleg- "be slack, be languid"). Medial -x- in Latin tends to become -ss- or -s- in French (compare cuisse from coxa). The Latin verb also is the source of Spanish laxar; Italian lasciare "leave," lassare "loosen."

Compare release (v.). Meaning "to grant the temporary possession of at a fixed rate" is from 1560s. Related: Leased; leasing. The form has been influenced by the noun, and the modern sense of "to take a lease" might be a new 19c. formation. Lessor, lessee in contract language preserve the Anglo-French vowel.