To do with a contest (5)
I believe the answer is:
about
'to do with a contest' is the definition.
I can't judge whether this definition defines the answer.
'with a contest' is the wordplay.
'with' means one lot of letters go next to another.
'contest' becomes 'bout' (boxing contest).
'a'+'bout' is 'ABOUT'.
Can you help me to learn more?
(Other definitions for about that I've seen before include "round" , "Concerned with" , "Apropos, concerning" , "On the topic of" , "Circa" .)