1530s, "one's proper work or purpose; power of acting in a specific proper way," from French fonction (16c.) and directly from Latin functionem (nominative functio) "a performance, an execution," noun of action from funct-, past-participle stem of fungi "perform, execute, discharge," from PIE *bhung- "be of use, be used" (source also of Sanskrit bhunjate "to benefit, make benefit, atone," Armenian bowcanem "to feed," Old Irish bongaid "to break, harvest"), which is perhaps related to root *bhrug- "to enjoy." Meaning "official ceremony" is from 1630s, originally in church use. Use in mathematics probably was begun by Leibnitz (1692). In reference to computer operations, 1947.
1844, "perform a function" (intransitive), from function (n.). Related: Functioned; functioning.
"dead, deceased, extinct," 1590s, from Old French defunct (14c., Modern French defunt) or directly from Latin defunctus "dead," literally "off-duty," past-participle adjective from defungi "to discharge, finish," from de- "off, completely" (see de-) + fungi "perform or discharge duty" (see function (n.)).
"done mechanically or without interest or zeal and merely for the sake of being rid of the duty of doing it; done so as to conform to the letter but not the spirit," 1580s, from Late Latin perfunctorius "careless, negligent," literally "like one who wishes to get through a thing," from Latin perfungus, past participle of perfungi "discharge, busy oneself, get through," from per "through" (from PIE root *per- (1) "forward," hence "through") + fungi "perform" (see function (n.)). Related: Perfunctorily.