WordWeb Online

1. Not worthy of notice
   "The insignificant young man entered the room";
   - undistinguished
    
2. Signifying nothing
   "insignificant sounds"
    
3. Of little importance, influence or power; of minor status
   "a minor, insignificant bureaucrat";
   - peanut
    
4. Devoid of importance, meaning, or force
   - unimportant

See also: flimsy, fragile, hole-and-corner, hole-in-corner, inappreciable, light, meaningless, minor, nonmeaningful, significance, slight, superficial, tenuous, thin, trivial, unimportant, unnoticeable

Antonym: significant