"one who grants a lease," late 14c., from Anglo-French lessor (late 13c.), from verb lesser "to let, to leave" (10c., Modern French laisser), from Latin laxare, from laxus "loose" (from PIE root *sleg- "be slack, be languid").
Entries linking to lessor
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).
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.