assignation (n.)

early 14c., "appointment by authority," from Old French assignacion (14c., Modern French assignation), from Latin assignationem (nominative assignatio) "an assigning, allotment," noun of action from past-participle stem of assignare/adsignare "to mark out, to allot by sign, assign, award," from ad "to" (see ad-) + signare "make a sign," from signum "identifying mark, sign" (see sign (n.)).

Meaning "action of legally transferring" (a right or property) is from 1570s; that of "a meeting by arrangement, tryst" is from 1650s, especially for a love-affair; assignation-house (1849) was an old euphemism for "brothel."