definition of
sub

[1] #1 sub v. [substitute, stand in, fill in] 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". wn

[2] #2 sub n. [bomber, grinder, hero, hero sandwich, hoagie, hoagy, Cuban sandwich, Italian sandwich, poor boy, submarine, submarine sandwich, torpedo, wedge, zep] 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. wn

[3] #3 sub n. [submarine, pigboat, U-boat] a submersible warship usually armed with torpedoes. wn