Was able to start up in frosty conditions (5)
I believe the answer is:
could
'was able' is the definition.
(I've seen this in another clue)
'to start up in frosty conditions' is the wordplay.
'to start' suggests taking the first letters.
'in' indicates putting letters inside.
'frosty conditions' becomes 'cold' (I can't explain this - if you can you should believe this answer much more).
The initial letter of 'up' is 'u'.
'u' put inside 'cold' is 'COULD'.
Can you help me to learn more?
(Another definition for could that I've seen is " Was able to (do something)".)