"official appointed to investigate complaints by individuals against institutions or authorities," 1959, from Swedish ombudsman, literally "commission man" (specifically in reference to the office of justitieombudsmannen, which heard and investigated complaints by individuals against abuses of the state); cognate with Old Norse umboðsmaðr, from umboð "commission" (from um- "around," from Proto-Germanic umbi, from PIE root *ambhi- "around," + boð "command," from PIE root *bheudh- "be aware, make aware") + maðr "man" (from PIE root *man- (1) "man").
mid-12c., "authorized representative of the Pope," from Old French legat and directly from Latin legatus "ambassador, envoy," originally "provided with a commission," past participle of legare "send as a deputy, send with a commission, charge, bequeath," possibly literally "engage by contract" and related to lex (genitive legis) "contract, law," from PIE root *leg- (1) "to collect, gather." General sense of "ambassador, delegate, messenger of a state or authority" is from late 14c. in English. Related: Legator; legatee; legatine.
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.