Makes keener ahead of time, I assure you (6)
I believe the answer is:
honest
'i assure you' is the definition.
I can't tell whether this defines the answer.
'makes keener ahead of time' is the wordplay.
'makes keener' becomes 'hones' (I've seen this in another clue).
'ahead of' means one lot of letters go next to another (some letters go in front of others).
'time' becomes 't' (abbreviation).
'hones'+'t'='HONEST'
Can you help me to learn more?
(Other definitions for honest that I've seen before include "Objective mediator" , "Fair and free of deceit" , "Truthful and dependable" , "Frank" , "Honourable, sincere" .)