... have some idea, doubtless, but no life (4)
I believe the answer is:
dead
'no life' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'have some idea doubtless' is the wordplay.
'DEAD' is hidden within the letters.
However, I'm not sure how the hidden word is indicated.
'but' is the link.
Can you help me to learn more?
(Other definitions for dead that I've seen before include "Lookalike" , "Lifeless" , "Defunct" , "Inanimate" , "Passed on" .)