This cover has a pothole in it (3,4)
I believe the answer is:
tea cosy
'this cover has a pothole in it' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?
'this cover has a pothole in' is the wordplay.
'this cover' becomes 'cosy' (as in a tea cosy).
'has' means one lot of letters go next to another.
'a pothole in' becomes 'tea' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'cosy' after 'tea' is 'TEA-COSY'.
Can you help me to learn more?
(Other definitions for tea cosy that I've seen before include "put on for warmth" , "It keeps the beverage hot" , "leaves in a hot state in this?" , "Pot cover" , "Knitted item" .)