Simpleton to spend time idly about river (5)
I believe the answer is:
moron
'simpleton' is the definition.
(I know that moron is a type of simpleton)
'spend time idly about river' is the wordplay.
I cannot quite understand how this works, but
'about' could be 'on' (as in a book 'on' a certain topic) and 'on' is present in the answer.
'river' could be 'r' (abbreviation) and 'r' is present in the answer.
The remaining letters 'mo' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'to' acts as a link.
Can you help me to learn more?
(Other definitions for moron that I've seen before include "Somewhat feeble-minded person" , "Blockhead" , "Foolish or stupid person" , "Halfwit" , "Fool" .)