"stern or aftermost deck of a ship," c. 1400, from Old French poupe "stern of a ship" (14c.), from Old Provençal or Italian poppa, from Latin puppis "poop, stern," a word of uncertain origin. Also "a deck above the ordinary deck on the aftermost part of a ship." As a verb, "to break heavily over the stern of a ship" (of waves, etc.). Poop deck is attested by 1779.
"excrement," 1744, a children's euphemism, probably of imitative origin. The verb in this sense is from 1903, but the same word in the sense "to break wind softly" is attested from 1721; earlier "to make a short blast on a horn" (poupen, late 14c.). Meaning "stupid or dull person" is from 1915, but this is perhaps short for nincompoop. Pooper-scooper is attested from 1970.
"up-to-date information," 1941, in poop sheet, U.S. Army slang, of unknown origin, perhaps from poop (n.2).
"become tired," 1931, of unknown origin (see pooped). With out (adv.) by 1934. Related: Pooping.