Something to batten down? (5)
I believe the answer is:
hatch
'batten down?' is the 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?
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for hatch that I've seen before include "Devise" , "Think up" , "Sit on eggs" , "Mountain goat" , "contrive to > emerge in > shade" .)