It's used in many long-legged girls' stockings (5)
I believe the answer is:
nylon
'it's used in many long-legged girls' stockings' is the definition.
I can't tell whether this definition defines the answer.
'it's used in many long-legged' is the wordplay.
'it's used in' says the answer is hidden in the clue.
'NYLON' can be found hidden inside 'many long legged'.
Can you help me to learn more?
(Other definitions for nylon that I've seen before include "Strong, resilient, synthetic fibre" , "Unaccompanied part song" , "Artificial material" , "Man-made material" , "Synthetic cloth" .)