I'd always thought catapult involved the meaning "to throw" or something like that, so i checked wikipedia. The entry for "catapult" says "The name is derived from the Greek κατα (against) and βαλλειν (to hurl (a missile))." Dictionary.com agrees with "[Origin: 1570–80; < L catapulta < Gk katapéltēs, equiv. to kata- cata- + péltēs hurler, akin to pállein to hurl]" However wikipedia _also_ has an entry on "catapulta" saying "A catapulta was an ancient military machine for throwing arrows and javelins, 12 or 15 feet long, at the enemy. The name comes from the Greek (katapeltes), because it could pierce a shield (pelta)."
Some random web searches result in both "kata = through, pelta = small shield" and "'kata' meaning 'against' and 'pallein' meaning 'to hurl, cast'." The later seems to be a more common derivation than the former though that may or may not mean anything. So either someone's confused in their derivation or we somehow got the same identical results from two different routes.