International athlete drinks more fluid (7)
I believe the answer is:
runnier
'more fluid' is the definition.
(runny can mean fluid or liquid)
'international athlete drinks' is the wordplay.
I cannot quite see how this works, but
'international' could be 'un' (I've seen this in other clues) and 'un' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for runnier that I've seen before include "More liquid" , "becomes more fluid ..." .)