significant - (adj.): something significant has an important effect or influence, especially on what will happen in the future

• Synonyms: important, meaningful, a big deal, noteworthy, powerful, major
• Antonyms: unimportant, meaningless, minor
• Origin: L. significantia meaning "meaning, force, energy" (yes, meaning!)
• Example: Today is a significant day in math.  We will be starting our unit on multiplication!