Remove son from trial: that’s sufficient (5)
I believe the answer is:
ample
'sufficient' is the definition.
(both can mean enough)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for ample that I've seen before include "Copious - abundant" , "Easily sufficient" , "Generous" , "Big" , "Large enough" .)