Rude wife showed the way to guards (4)
I believe the answer is:
lewd
'rude' is the definition.
(thesaurus)
'wife showed the way to guards' is the wordplay.
'wife' becomes 'w' (abbreviation).
'showed the way' becomes 'led' (lead can mean to show someone the way).
'to guards' is an insertion indicator (inserted letters are guarded).
'w' placed inside 'led' is 'LEWD'.
(Other definitions for lewd that I've seen before include "Smutty" , "Indecent and vulgar (4)" , "Weld in lascivious way" , "Obscene, indecent" , "suggestive manner" .)