Not yet decided to start (4)
I believe the answer is:
open
'start' is the definition.
(I know that open is a more specific form of the action start)
'not yet decided' is the wordplay.
'not' becomes 'o' (I've seen this in other clues).
'yet decided' becomes 'pen' (I can't justify this - if you can you should believe this answer much more).
'o'+'pen'='OPEN'
'to' is the link.
Can you help me to learn more?
(Other definitions for open that I've seen before include "Not secret or hidden" , "Ready for business; spread out; manifest" , "Willing" , "Frank and unlocked" , "Allowing entry and exit" .)