Fastening in accordance (4)
I believe the answer is:
cord
'fastening' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'in accordance' is the wordplay.
'in' indicates a hidden word.
'CORD' is hidden within 'accordance'.
Can you help me to learn more?
(Other definitions for cord that I've seen before include "Thin rope" , "Line of twisted fibres or threads" , "Small rope or thick string" , "Thin string" , "Small rope; flex" .)