sub

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A substitute.
• intransitive verb To act as a substitute.
• intransitive verb To put or use (a person or thing) as a substitute.
• noun Nautical A submarine.
• noun A submarine sandwich.

from The Century Dictionary.

• noun A prefix of Latin origin, meaning ‘under, below, beneath,’ or ‘from under.’
• noun A substitute; specifically, one who is willing to serve as a substitute for a regular compositor on a newspaper.
• To act as a substitute; specifically, to act as the substitute of another in a composing-room.
• To subirrigate. See subbing, 2.
• An abbreviation of subject
• of substitute
• of suburb
• of suburban.
• noun A subaltern; a subordinate.

from the GNU version of the Collaborative International Dictionary of English.

• noun colloq. A subordinate; a subaltern.
• noun a shortened form of submarine, the boat.
• noun a shortened form of submarine sandwich; also called hero, hero sandwich, and grinder.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• preposition Under.
• verb To coat with a layer of adhering material; to planarize by means of such a coating.
• verb microscopy To prepare (a slide) with an layer of transparent substance to support and/or fix the sample.
• noun A submarine.
• noun A submarine sandwich—a sandwich made on a long bun.
• noun US, informal A substitute.
• noun UK, informal A substitute in a football (soccer) game: someone who comes on in place of another player part way through the game.
• noun UK, informal, often in plural Short for subscription: a payment made for membership of a club, etc.
• noun informal A submissive in BDSM practices.
• noun Internet, informal Short for subtitle.
• noun computing, programming A subroutine (sometimes one that does not return a value, as distinguished from a function, which does).
• noun colloquial, dated A subordinate.
• noun colloquial, dated A subaltern.
• verb US, informal To substitute for.
• verb US, informal To work as a substitute teacher, especially in primary and secondary education.
• verb UK, informal (soccer) To replace (a player) with a substitute.
• verb UK, informal (soccer) Less commonly, and often as sub on, to bring on (a player) as a substitute.
• verb UK To perform the work of a subeditor or copy editor; to subedit.
• verb UK, slang, transitive To lend.
• verb slang, intransitive To subscribe.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb be a substitute
• noun a submersible warship usually armed with torpedoes
• noun 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