From WordNet (r) 3.0 (2006):
sub
n 1: a large sandwich made of a long crusty roll split
lengthwise and filled with meats and cheese (and tomato and
onion and lettuce and condiments); different names are used
in different sections of the United States [syn: bomber,
grinder, hero, hero sandwich, hoagie, hoagy,
Cuban sandwich, Italian sandwich, poor boy, sub,
submarine, submarine sandwich, torpedo, wedge,
zep]
2: a submersible warship usually armed with torpedoes [syn:
submarine, pigboat, sub, U-boat]
v 1: be a substitute; "The young teacher had to substitute for
the sick colleague"; "The skim milk substitutes for cream--
we are on a strict diet" [syn: substitute, sub, stand
in, fill in]