It starts here (5)
I believe the answer is:
aitch
'it starts here' is the definition.
The definition suggests a singular noun which matches the answer.
This is all the clue.
Can you help me to learn more?
(Other definitions for aitch that I've seen before include "Aspirated letter" , "It's dropped by Cockneys" , "The letter h in full" , "first bit of hymn?" , "bone" .)