Analyse and understand river-dwelling fish (6)
I believe the answer is:
decode
'analyse' is the definition.
The definition and answer can be both related to thinking as well as being verbs in their base form.
Perhaps there's a link between them I don't understand?
'understand river-dwelling fish' is the wordplay.
I cannot quite see how this works, but
'fish' could be 'cod' (type of fish) and 'cod' is present in the answer.
'river' could be 'dee' (River Dee) and 'dee' is found within the remaining letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'and' acts as a link.
Can you help me to learn more?
(Other definitions for decode that I've seen before include "Crack (a secret message)" , "Put in" , "Penetrate or solve encrypted message" , "Get cracking" , "Find hidden meaning" .)