jetsam n.

1848, "to throw overboard," especially to save a ship in danger, from jettison (n.) "act of throwing overboard" to lighten a ship. This noun was an 18c. Marine Insurance writers' restoration of the earlier form and original sense of the 15c. word that had become jetsam, probably because jetsam had taken on a sense of "things cast overboard" and an unambiguous word was needed for "act of casting things overboard."

Middle English jetteson (n.) "act of throwing overboard" is from Anglo-French getteson, Old French getaison "act of throwing (goods overboard)," especially to lighten a ship in distress, from Late Latin iactationem (nominative iactatio) "a throwing, act of throwing," noun of action from past participle stem of iactare "to throw, toss about" (from PIE root *ye- "to throw, impel"). Related: Jettisoned.

c. 1600, from Anglo-French floteson, from Old French flotaison "a floating" (Modern French flottaison), from floter "to float, set afloat" (of Germanic origin and cognate with float) + -aison, from Latin -ation(em). Spelled flotsen in English till mid-19c. when it altered, perhaps under influence of many English words in -some. Folk-etymologized in dialect as floatsome.

In British law, flotsam are goods found floating on the sea as a consequence of a shipwreck or action of wind or waves; jetsam are things cast out of a ship in danger of being wrecked, and afterward washed ashore, or things cast ashore by the sailors. Whatever sinks is lagan. Flotsam and jetsam figuratively for "odds and ends" is attested by 1861.

*yē-, Proto-Indo-European root meaning "to throw, impel."

It forms all or part of: abject; abjection; adjacence; adjacent; adjective; aphetic; catheter; circumjacent; conjecture; deject; ease; ejaculate; eject; enema; gist; ictus; interjacent; inject; interject; interjection; jess; jet (v.1) "to sprout or spurt forth, shoot out;" jet (n.1) "stream of water;" jete; jetsam; jettison; jetton; jetty (n.) "pier;" joist; jut; object; objection; objective; paresis; project; projectile; reject; rejection; subjacent; subject; subjective; trajectory.

It is the hypothetical source of/evidence for its existence is provided by: Hittite ijami "I make;" Latin iacere "to throw, cast."