Deceive a thousand ladies naughtily (7)
I believe the answer is:
mislead
'deceive' is the definition.
(thesaurus)
'a thousand ladies naughtily' is the wordplay.
'a thousand' becomes 'm' ('M' can be a synonym of 'thousand'**).
'naughtily' indicates anagramming the letters.
'ladies' is an anagram of 'islead'.
'm'+'islead'='MISLEAD'
(Other definitions for mislead that I've seen before include "Deceive" , "Cause someone to believe something is not true" , "Take someone in the wrong direction" , "Hoodwink" , "Fool" .)