Quadrilateral with four sides of equal length (5)

I believe the answer is:

rhomb

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'quadrilateral' is the definition.
(I know that rhomb is a type of parallelogram)

I can't explain the remainder of the clue.

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(Other definitions for rhomb that I've seen before include "Crystal with six faces having parallel edges" , "Four-sided figure" , "Figure of four equal sides" , "Crystal shape" , "Quadrilateral with four equal sides" .)

I've seen this clue in The Times.

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