The decade for neckwear? (7)
I believe the answer is:
forties
'the decade' is the definition.
(eg the 1940s)
'for neckwear?' is the wordplay.
'neckwear?' becomes 'ties' (I've seen this in another clue).
'for'+'ties'='FORTIES'
(Other definitions for forties that I've seen before include "The age" , "British shipping forecast area" , "See 25 Across" .)