The word Slippernes is misspelled against Slipperness, a noun meaning "Slipperiness."
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Slipperness 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:  slipperne-s 
Correct Spelling:  slipperne-ss 
Find more wrongly spelled words of Slipperness to spell it well.