Understir or Understair: How To spell?

The word Understir is misspelled against Understair, an adjective meaning "pertaining to the kitchen, the servants' quarters; hence, subdinate; menial."

Word contains consecutive vowels 'AI' in between alphabets underst & r is misspelled as 'I'
Wrong Spelling:  underst-i-r 
Correct Spelling:  underst-ai-r 
Find more wrongly spelled words of Understair to spell it well.

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