When fastened, gave way (7)
I believe the answer is:
buckled
This clue might be a double definition.
'when fastened' is the first definition.
'buckled' can be an answer for 'fastened' (buckling is a kind of fastening). I am not sure about the 'when' bit.
'gave way' is the second definition.
(buckling is a kind of giving way)
Can you help me to learn more?
(Other definitions for buckled that I've seen before include "collapsed" , "Bent" , "Securely fastened" , "folded under pressure" , "Crumpled under pressure." .)