Significant Meaning:  Important, sufficiently great.

Synonyms: eloquent, expressive, convincing, indicative, etc.
Antonyms: insignificant, trivial, meaningless, unimportant, etc.

Example: 

1) That is a significant amount and will help support hundreds of local businesses.
2) Many cities, Saratoga Springs among them, have significant downtown populations.
3) There is also a significant disconnect between academic accounting and practice.
4) A significant advantage Apple has been able to maintain is software reliability.