Endlessly evaluate idiots (5)
I believe the answer is:
asses
'idiots' is the definition.
(I've seen this before)
'endlessly evaluate' is the wordplay.
'endlessly' means to remove the last letter.
'evaluate' becomes 'assess' (synonyms).
'assess' with its last letter taken off is 'ASSES'.
(Other definitions for asses that I've seen before include "Stupid people; Roman coins" , "Dolts" , "dim bulbs?" , "Fools; animals" , "Donkeys" .)