Confident visionary said alternative's not on at first (10)
I believe the answer is:
optimistic
'confident' is the definition.
(thesaurus)
'visionary said alternative's not on at first' is the wordplay.
I cannot quite understand how this works, but
'said' could be 't' (I've seen this in other clues) and 't' is located in the answer.
'not' could be 'o' (I've seen this in other clues) and 'o' is found within the answer.
'first' could be 'ist' (ist resembles 1st) and 'ist' is located in the answer.
This explanation may well be incorrect...
(Other definitions for optimistic that I've seen before include "Hopeful and confident" , "Happy-go-lucky" , "Pollyannaish" , "Looking on the bright side" , "Hopeful about the future" .)