1610s, "action of delegating" (earlier in this sense was delegacie, mid-15c.); perhaps a native formation, perhaps from French délégation, or directly from Latin delegationem (nominative delegatio) "assignment, delegation," noun of action from past-participle stem of delegare "to send as a representative," from de "from, away" (see de-) + legare "send with a commission," possibly literally "engage by contract" and related to lex (genitive legis) "contract, law," from PIE root *leg- (1) "to collect, gather." Meaning "persons sent by commission" is from 1818; meaning "a state's elected representatives, taken collectively," is U.S. political usage from 1828.
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).
mid-14c., "authority entrusted to someone, delegated authority or power," from Old French commission and directly from Latin commissionem (nominative commissio) "act of committing," in Medieval Latin "delegation of business," noun of action from past participle stem of committere "to unite, connect, combine; to bring together," from com "with, together" (see com-) + mittere "to release, let go; send, throw" (see mission).
Meaning "document delegating authority" is from early 15c.; meaning "body of persons charged with authority for the performance of certain special duties" is from late 15c. Sense of "anything entrusted to anyone to perform" is from 1560s; sense of "act of committing or doing" is from 1590s.
Naval sense "period of active service of a warship" is by 1882 (in commission "under the command of an officer" is from 1733). Hence out of commission "laid up in a navy yard or in reserve" (1878), subsequently extended to other machinery, and, figuratively, to persons or human qualities by 1917.
In commercial use, "authority delegated by another for the purchase and sale of goods," 1620s. Meaning "allowance made or percentage given to an agent for transacting business" is from 1725.