Fit into a bore (4)
I believe the answer is:
well
This clue is a double definition.
'fit' is the first definition.
(associated in meaning)
'a bore' is the second definition.
(I've seen this before)
'into' acts as a link.
(Other definitions for well that I've seen before include "rise up" , "Source; in good health" , "Healthy; extremely" , "Fine - drilled hole" , "Competently" .)