"Hat," not "bat" (6)
I believe the answer is:
bowler
This clue could be a double definition.
'hat' is the first definition.
(I know that bowler is a type of hat)
'bat' is the second definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'not' is the link.
Can you help me to learn more?
(Other definitions for bowler that I've seen before include "Derby" , "Hard felt hat" , "Posh hat or cricket player" , "9's role" , "He likes a flat green" .)