Spike or Jimmy, perhaps (4)
I believe the answer is:
nail
'spike' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for nail that I've seen before include "thing for keeping things together" , "Measure of cloth" , "Perfectly execute" , "Spike, tack" , "Spike, fasten" .)