Step on it before the opening (7)
I believe the answer is:
doormat
'step' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'on it before the opening' is the wordplay.
I cannot really see how this works, but
'on' could be 'at' (I've seen this in other clues) and 'at' is present in the answer.
'opening' could be 'door' (I've seen this in another clue) and 'door' is present in the answer.
A single letter 'm' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for doormat that I've seen before include "Badly treated but uncomplaining person" , "dull submissive type" , "seen walking in?" , "Habitually humiliated person" , "Carpet protector or very submissive person" .)