certain

American Heritage® Dictionary of the English Language, Fourth Edition

1. adj. Definite; fixed: set aside a certain sum each week.
2. adj. Sure to come or happen; inevitable: certain success.
3. adj. Established beyond doubt or question; indisputable: What is certain is that every effect must have a cause.
4. adj. Capable of being relied on; dependable: a quick and certain remedy.
5. adj. Having or showing confidence; assured.
6. adj. Not specified or identified but assumed to be known: felt that certain breeds did not make good pets.
7. adj. Named but not known or previously mentioned: a certain Ms. Johnson.
8. adj. Perceptible; noticeable: a certain charm; a certain air of mystery.
9. adj. Not great; calculable: to a certain degree; a certain delay in the schedule.
10. pro. An indefinite but limited number; some: Certain of the products are faulty.
11. idiom. for certain Without doubt; definitely.

Century Dictionary and Cyclopedia

1. Fixed; determinate; definite; specified; prescribed; settled beforehand: as in the phrase “at a time certain.”
2. Indefinite in the sense of not being specifically named; known but not described: applied to one or more real individual objects or characters, as distinguished from a class of objects or an order of characters; coming under particular observation, but undefined, as to kind, number, quantity, duration, etc.; some particular: as, a lady of a certain age.
3. Some (known but unspecified): followed by of.
4. Established as true or sure; placed beyond doubt; positively ascertained and known; unquestionable; indisputable.
5. Capable of being depended on; trustworthy.
6. Unfailing; unerring; sure; positive: as, a certain remedy for rheumatism.
7. Assured; free from doubt regarding: used absolutely, or with of, and formerly sometimes with on.
8. Sure: with an infinitive: as, he is certain to be there to-morrow.
9. Synonyms Undeniable, unquestionable, undoubted, indubitable, indisputable, incontrovertible, inevitable. Sure, Positive, Certain, Confident, etc. (see confident); unhesitating, undoubting.
10. n. A definite but unstated quantity.
11. n. Certainty.
12. n. In the Roman Catholic Church, prayers said daily at mass for specified persons, as for the members of a guild unable to keep a priest of its own, but who paid so much to a church to have a daily remembrance. Also certainty.
13. Certainly; assuredly.

Wiktionary

1. adj. Sure, positive, not doubting.
2. Having been determined but unspecified. The quality of some particular subject or object which is known by the speaker to have been specifically singled out among similar entities of its class.

GNU Webster's 1913

1. adj. Assured in mind; having no doubts; free from suspicions concerning.
2. adj. Determined; resolved; -- used with an infinitive.
3. adj. Not to be doubted or denied; established as a fact.
4. adj. Actually existing; sure to happen; inevitable.
5. adj. Unfailing; infallible.
6. adj. Fixed or stated; regular; determinate.
7. adj. Not specifically named; indeterminate; indefinite; one or some; -- sometimes used independenty as a noun, and meaning certain persons.
8. n. obsolete Certainty.
9. n. obsolete A certain number or quantity.
10. adv. obsolete Certainly.

WordNet 3.0

1. adj. exercising or taking care great enough to bring assurance
2. adj. reliable in operation or effect
3. adj. having or feeling no doubt or uncertainty; confident and assured
4. adj. certain to occur; destined or inevitable
5. adj. definite but not specified or identified
6. adj. established beyond doubt or question; definitely known
7. adj. established irrevocably