Grumble about this hairdo (7)
I believe the answer is:
mohican
'grumble about this hairdo' is the definition.
The definition suggests a singular noun which matches the answer.
'grumble about this hairdo' is the wordplay.
'grumble' becomes 'moan' (I've seen this before).
'about' means one lot of letters goes inside another.
'this hairdo' becomes 'hic' (I can't justify this - if you can you should give a lot more credence to this answer).
'moan' going around 'hic' is 'MOHICAN'.
Can you help me to learn more?
(Other definitions for mohican that I've seen before include "American native, 9 [ > HAIRCUT]" , "Punk style" , "Hawk-eye went with" , "Haircut with only a band of hair down the middle of the scalp" , "A Native American people" .)