11 letters · 17 points in Scrabble
noun an apparatus intended for use under water
noun a warship designed to operate under water
adjective capable of being immersed in water or functioning while submerged
originEtymology tree English submerse Proto-Indo-European *-tḗr Proto-Indo-European *-dʰlom Proto-Indo-European *-dʰlis Proto-Italic *-ðlis Latin -bilis Latin -ibilis Old French -ibleder. Middle English -ible English -ible English submersible From submerse + -ible.
Etymology from Wiktionary, CC BY-SA 3.0