There's one H in "Haircut"! (7)
I believe the answer is:
shingle
'h in haircut' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'there's one' is the wordplay.
I cannot really understand how this works, but
'there's' could be 'n' (I've seen this in other clues) and 'n' is present in the answer.
'one' could be 'i' (Roman numeral) and 'i' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for shingle that I've seen before include "Bob" , "'hairdo'" , "Mass of small rounded pebbles" , "on the roof?" , "A tile; some beach" .)