bad

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

• adjective Not achieving an adequate standard; poor.
• adjective Immoral or evil.
• adjective Vulgar or obscene.
• adjective Disobedient or naughty.
• adjective Disagreeable, unpleasant, or disturbing.
• adjective Unfavorable.
• adjective Not fresh; rotten or spoiled.
• adjective Injurious in effect; detrimental.
• adjective Not working properly; defective.
• adjective Full of or exhibiting faults or errors.
• adjective Having no validity; void.
• adjective Being so far behind in repayment as to be considered a loss.
• adjective Severe; intense.
• adjective Being in poor health or in pain.
• adjective Being in poor condition; diseased.
• adjective Sorry; regretful.
• adjective Slang Very good; great.
• noun Something that is below standard or expectations, as of ethics or decency.
• adverb Badly.
• idiom (in bad) In trouble or disfavor.
• idiom (my bad) Used to acknowledge that one is at fault.
• idiom (half/so) Reasonably good.
• idiom (that's too bad) Used to express sadness or sympathy.
• idiom (that's too bad) Used in response to a protest or complaint to express insistence that the speaker's expectation be met.

from The Century Dictionary.

• noun Preterit of bid.
• Evil; ill; vicious; wicked; depraved: applied to persons, conduct, character, influence, etc.: as, a bad man; bad conduct; a bad life; a bad heart; bad influence, etc.
• Offensive; disagreeable; troublesome; painful; grievous: as, bad treatment; a bad temper; it is too bad that you had to wait so long.
• Hurtful; noxious; having an injurious or unfavorable tendency or effect: with for: as, bad air or bad food; late hours are bad for the health; this step would be bad for your reputation or prospects.
• Ill; in ill health; sick; in unsound condition: as, to feel bad; to be bad with rheumatism; a bad hand or leg.
• Not good; defective; worthless; poor; of no value: as, bad coin; bad debts; a bad soil; a bad crop; a bad piece of work; bad health.
• Incorrect; faulty: as, a bad aim; bad English; a bad pronunciation.
• Not valid; not sound: as, a bad claim; a bad plea.
• Unfavorable; unfortunate: as, bad news; bad success.
• [Bad is the ordinary antithesis of good, in all its senses, whether positively, ‘evil,’ ‘harmful,’ or negatively, ‘not good,’ ‘not satisfactory,’ and whether substantively, ‘being evil,’ or causally, ‘causing harm.’ The senses run into one another, the precise application being determined by the context.]
• noun That which is bad. A bad condition: as, to go to the bad (see below). A bad thing: as, there are bads and goods among them.

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

• imperative obsolete Bade.
• adjective Wanting good qualities, whether physical or moral; injurious, hurtful, inconvenient, offensive, painful, unfavorable, or defective, either physically or morally; evil; vicious; wicked; -- the opposite of good.

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

• adjective this sense?) (slang) Fantastic.
• verb archaic Alternative past tense of bid. See bade.
• verb UK, dialect, transitive To shell (a walnut).
• adjective Not good; unfavorable; negative.
• adjective Seemingly non-appropriate, in manners, etc.
• adjective Not suitable or fitting.
• adjective Tricky; stressful; unpleasant.
• adjective Evil; wicked.
• adjective Faulty; not functional.
• adjective of food Spoiled, rotten, overripe.
• adjective Malodorous, foul.