Submarine

wiktionary

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sub- +‎  marine.  Doublet of  Fomorian. 

etymonline

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submarine (adj.)

1640s, from sub- + marine (adj.).

submarine (n.)

"submarine boat," 1899, from submarine (adj.), perhaps short for earlier submarine vessel (1732), etc. Earlier "a creature living under the sea" (1703). The short form sub is attested from 1917. As a type of sandwich from 1955, so called from the shape of the roll. Related: Submariner.