Cool tip I note to cut hair (10)
I believe the answer is:
trendiness
'cool tip i' is the definition.
The definition suggests a singular noun which matches the answer.
'note to cut hair' is the wordplay.
'note' becomes 'endin' (I can't explain this - if you can you should give a lot more credence to this answer).
'to cut' indicates putting letters inside (some letters cut their way into a word).
'hair' becomes 'tress' (tress is a kind of hair).
'endin' placed inside 'tress' is 'TRENDINESS'.
Can you help me to learn more?
(Another definition for trendiness that I've seen is " high fashion".)