sub

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Informal See submarine.
2. n. Informal See submarine. See Regional Note at submarine.
3. n. A substitute.
4. v. To act as a substitute.

Century Dictionary and Cyclopedia

1. n. A prefix of Latin origin, meaning ‘under, below, beneath,’ or ‘from under.’ It occurs in its literal sense in many words, verbs, adjectives, and nouns, taken from the Latin, as in subjacent, underlying, subscribe, underwrite, subside, sit down, submerge, plunge down, etc., the literal sense being in many cases not felt in English, as in subject, subjoin, subtract, etc.
2. n. A subaltern; a subordinate.
3. n. A substitute; specifically, one who is willing to serve as a substitute for a regular compositor on a newspaper.
4. To act as a substitute; specifically, to act as the substitute of another in a composing-room.
5. To subirrigate. See subbing, 2.
6. An abbreviation of subject
7. of substitute
8. of suburb
9. of suburban.

Wiktionary

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

GNU Webster's 1913

1. n. colloq. A subordinate; a subaltern.
2. n. a shortened form of submarine, the boat.
3. n. a shortened form of submarine sandwich; also called hero, hero sandwich, and grinder.

WordNet 3.0

1. v. be a substitute
2. n. a submersible warship usually armed with torpedoes
3. n. 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