early 15c., "one appointed to perform some business by a commission from a proper authority," from Anglo-French commissionaire, from or on the model of Medieval Latin commissionarius "one entrusted with a commission," from commissionem "act of committing," in Medieval Latin "delegation of business" (see commission (n.)).
Meaning "member of a commission" is from 1530s, especially "person elected to manage the affairs of a municipality." Short form commish is attested by 1910 (earlier it was short for commission).
