Understirs or Understairs: How To spell?

The word Understirs is misspelled against Understairs, a noun meaning "The basement or cellar."

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

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