Consume in one attempt (3)
I believe the answer is:
Here is my best explanation:
'consume' is the definition.
(eating is a kind of consuming)
'in one attempt' is the subsidiary indication.
'in' indicates a hidden word.
'eat' is hidden in the letters of 'one attempt'.
(Other definitions for eat that I've seen before include "Bit, chew and swallow", "to do etching?", "Have a meal", "put away", "consume", "Use a knife and fork", "Do cats - bats? Do bats - cats? (Alice in Wonderland)", "Dine in a restaurant", "get stuck in" and "Feed".)