The word Restiffnes is misspelled against Restiffness, a noun meaning "Restiveness."
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Restiffness has double 'ss' in the end mispronounced as 's'
Remember double 'SS' appears in the end of this word which should not be misspelled with single 'S'
Wrong Spelling:  restiffne-s 
Correct Spelling:  restiffne-ss 
Find more wrongly spelled words of Restiffness to spell it well.