An eagle perhaps heard devouring small cuckoo (6)
I believe the answer is:
absurd
'heard devouring small cuckoo' is the definition.
The answer and definition are not the same part of speech. However, past participle verbs and adjectives sometimes mean the same thing.
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for absurd that I've seen before include "Quite ridiculous, silly" , "'Derisory, cockeyed (6)'" , "Arousing derision" , "'Ridiculous, silly (6)'" , "Ludicrous, silly" .)