Undergarment found in library! (3)
I believe the answer is:
bra
'undergarment' is the definition.
(I've seen this before)
'in library' is the wordplay.
'in' says the answer is hidden in the clue.
'BRA' is hidden within 'library'.
'found' acts as a link.
(Other definitions for bra that I've seen before include "support" , "Female undergarment" , "one carrying chest" , "I give a couple a lift" , "Underwear item" .)