This will do for a start (6)
I believe the answer is:
origin
'a start' is the definition.
(I've seen this in another clue)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for origin that I've seen before include "Place where something begins" , "Source - provenance" , "Where axes cut" , "Source, beginning point" , "spring" .)