importance : Idioms & Phrases

• noun an inflated feeling of pride in your superiority to others
  ego; egotism.
  
• noun an exaggerated opinion of your own importance
  swelled head; egotism.
  

WordNet

Self`-im*por"tance noun

Definitions

1. An exaggerated estimate of one's own importance or merit, esp. as manifested by the conduct or manners; self-conceit.

Webster 1913