significant

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

• adjective Having or expressing a meaning.
• adjective Having or expressing a covert or nonverbal meaning; suggestive.
• adjective Having or likely to have a major effect; important.
• adjective Fairly large in amount or quantity.
• adjective Statistics Of or relating to observations or occurrences that are too closely correlated to be attributed to chance and therefore indicate a systematic relationship.

from The Century Dictionary.

• Signifying something; conveying a meaning; having a purport; expressive; implying some character, and not merely denotative: as, a significant word or sound.
• Serving as a sign or indication; having a special or covert meaning; suggestive; meaning: as, a significant gesture; a significant look.
• Important; notable; weighty; more strictly, important for what it indicates, but also, often, important in its consequences: opposed to insignificant: as, a significant event.
• noun That which is significant; a meaning, sign, or indication.

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

• adjective Fitted or designed to signify or make known somethingl having a meaning; standing as a sign or token; expressive or suggestive.
• adjective Deserving to be considered; important; momentous.
• adjective (Arith.) the figures which remain to any number, or decimal fraction, after the ciphers at the right or left are canceled. .
• noun That which has significance; a sign; a token; a symbol.

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

• adjective Signifying something; carrying meaning.
• adjective Having a covert or hidden meaning
• adjective Having a noticeable or major effect; notable
• adjective Reasonably large in number or amount
• adjective statistics Having a low probability of occurring by chance (for example, having high correlation and thus likely to be related).
• noun That which has significance; a sign; a token; a symbol.

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

• adjective too closely correlated to be attributed to chance and therefore indicating a systematic relation
• adjective important in effect or meaning
• adjective fairly large
• adjective rich in significance or implication