perquisite n.

mid-15c., "property acquired other than by inheritance" (c. 1300 in Anglo-Latin), from Medieval Latin perquisitum "thing gained, profit," in classical Latin, "thing sought after," noun use of neuter past participle of perquirere "to seek, ask for," from per "thoroughly" (see per) + quærere "to seek" (see query (v.)). For Latin vowel change, see acquisition. The general meaning "any incidental profit, gain, or fee on top of regular wages" is by 1560s.