Dowdiness primarily missing in tailored threads -- suit! (6)

I believe the answer is:

hearts

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'suit' is the definition.
(hearts is a playing card suit)

I can't explain the remainder of the clue.

(Other definitions for hearts that I've seen before include "Card suit and essential organs" , "Playing-card suit" , "Scots club nickname; suit" , "Cores" , "Major suit at cards" .)

I've seen this clue in The Telegraph.

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