Catch or fastener (4)
I believe the answer is:
nail
I believe this is a double definition.
'catch' is the first definition.
(nail can mean to catch or arrest)
'fastener' is the second definition.
(I know that nail is a type of fastener)
'or' acts as a link.
(Other definitions for nail that I've seen before include "Expose as a lie" , "Perfectly execute" , "metal fixture" , "Horny part of the digit" , "Fasten - detect and expose" .)