Passed off as a dark suit (6)
I believe the answer is:
spades
'a dark suit' is the definition.
(I've seen this in another clue)
'passed off' is the wordplay.
'off' indicates an anagram.
'passed' is an anagram of 'SPADES'.
'as' is the link.
(Other definitions for spades that I've seen before include "dark suit" , "Does some groundwork" , "those getting soiled?" , "Implements for a suit" , "Card suits and shovels" .)