sub

definition: a submersible warship usually armed with torpedoes
example:
speech part: noun
synonyms: submarine
definition: a large sandwich made of a long crusty roll split lengthwise and filled often filled with a combination of meats, cheese, tomato, onion, lettuce, and condiments
example: The local grocery store had the best subs where I grew up.
speech part: noun
synonyms: torpedo
definition: be a substitute
example: The young teacher had to substitute for the sick colleague
speech part: verb
synonyms: substitute

sub is explained and pronounced

How sub is being used?