What's often part of underwear, laciest pants (7)
I believe the answer is:
'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'.
Can you help me to learn more?
(Other definitions for elastic that I've seen before include "Castile (anag)" , "Material that stretches" , "Pliable" , "Flexible (material)" , "Able to stretch" .)