Fastening in wet conditions (5)
I believe the answer is:
twine
'fastening' is the definition.
'in wet conditions' is the wordplay.
'conditions' indicates anagramming the letters (letters must be in a new condition).
'in'+'wet'='inwet'
'inwet' with letters rearranged gives 'TWINE'.
(Other definitions for twine that I've seen before include "String of twisted fibres" , "Curl; string" , "Knot" , "can get into knots" , "Tough string" .)