noun

1. A boat that can go underwater.

2. A kind of sandwich made in a long loaf of bread.

3. Pitch delivered with an underhand motion.

Synonyms: U-boat, sub, grinder, hero, hoagie, hoagy, po' boy, poor boy

verb

1. To operate or serve on a submarine.

2. To torpedo; to destroy with a sudden sneak attack.

3. (sometimes figurative) To sink or submerge oneself.

adjective

1. Undersea.

2. Hidden or undisclosed.

   “a submarine patent”

3. Of a pitch, thrown with the hand lower than the elbow.