true

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

• adjective Consistent with fact or reality; not false or erroneous: synonym: real.
• adjective Not counterfeit; real or genuine: synonym: authentic.
• adjective Conforming to the characteristics or criteria of a group or type; typical.
• adjective Properly called.
• adjective Reliable; accurate.
• adjective Faithful, as to a friend, vow, or cause; loyal. synonym: faithful.
• adjective Archaic Truthful, honest, or trustworthy.
• adjective Sincerely felt or expressed; unfeigned.
• adjective Rightful; legitimate.
• adjective Exactly conforming to a rule, standard, or pattern.
• adjective Accurately shaped, fitted, or placed.
• adjective Determined with reference to the earth's axis, not the magnetic poles.
• adjective Quick and exact in sensing and responding.
• adjective Computers Indicating one of two possible values taken by a variable in Boolean logic or a binary device.
• adverb In accord with reality, fact, or truthfulness.
• adverb Unswervingly; exactly.
• adverb So as to conform to a type, standard, or pattern.
• transitive verb To position (something) so as to make it balanced, level, or square.
• noun Truth or reality. Used with the.
• noun Proper alignment or adjustment.

from The Century Dictionary.

• Conformable to fact; being in accordance with the actual state of things; not false, fictitious, or erroneous: as, a true story; a true statement.
• What proposition is there respecting human nature which is absolutely and universally true?
• Conformable to reason or to established rules or custom; exact; just; accurate; correct.
• Conformable to law and justice; legitimate; rightful: as, the true heir.
• Conformable to nature; natural; correct.
• In biology:
• Conforming or conformable to a type, norm, or standard of structure; typical; as, an amœba is a true animal; a canary is a true bird; the lion is a true cat; a frog or toad is not a true reptile.
• Genuine; truebred; not hybrid or mongrel: as, a true merino sheep. Also used adverbially: as, to breed true.
• Genuine; pure; real; not counterfeit, adulterated, false, or pretended.
• In anatomy, complete; perfected: as, true ribs (that is, those which articulate with the breastbone, as distinguished from false or floating ribs); the true pelvis (that part of the pelvis below the superior strait or iliopectineal line); a true corpus luteum (the complete corpus luteum of pregnancy, as distinguished from the same body unaffected by the result of conception).
• Free from falsehood; habitually speaking the truth; veracious; truthful.
• Firm or steady in adhering to promises, to friends, to one's principles, etc.; not fickle, false, or perfidious; faithful; constant; loyal.
• Honest.
• Sure; unerring; unfailing.
• Synonyms Veritable, actual. See reality.
• 8 and Sincere, honorable.
• noun Truth; fidelity.
• noun Agreement; covenant; pledge.
• noun A temporary cessation of war, according to agreement; respite from war; truce. See truce.
• noun in eccles. law, an expression formerly used at the end of each several article in the libel as descriptive of the charges therein contained.
• To verify.
• To make true in position, form, adjustment, or the like: give a right form to; adjust nicely; put a keen, fine, or smooth edge on; make exactly straight, square, plumb, level, or the like: a workmen's term.

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

• adverb In accordance with truth; truly.
• adjective Conformable to fact; in accordance with the actual state of things; correct; not false, erroneous, inaccurate, or the like.
• adjective Right to precision; conformable to a rule or pattern; exact; accurate.
• adjective Steady in adhering to friends, to promises, to a prince, or the like; unwavering; faithful; loyal; not false, fickle, or perfidious.
• adjective Actual; not counterfeit, adulterated, or pretended; genuine; pure; real.