What's often part of underwear, laciest pants (7)

I believe the answer is:

elastic

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'what's often part of underwear' is the definition.
I can't judge whether this defines the answer.

'laciest pants' is the wordplay.
'pants' indicates anagramming the letters (UK informal term for 'nonsense' or 'rubbish').
'laciest' with letters rearranged gives 'ELASTIC'.

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(Other definitions for elastic that I've seen before include "Castile (anag)" , "Material that stretches" , "Pliable" , "Flexible (material)" , "Able to stretch" .)

I've seen this clue in The Everyman puzzle in The Observer.

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