Bit of fish in river to provide meaning (6)
I believe the answer is:
define
'provide meaning' is the definition.
I can't tell whether this definition defines the answer.
'bit of fish in river' is the wordplay.
'bit of fish' becomes 'fin' ('fin' is part of 'fish').
'in' means one lot of letters goes inside another.
'river' becomes 'dee' (River Dee).
'fin' placed into 'dee' is 'DEFINE'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for define that I've seen before include "Specify" , "Give precise meaning" , "Demarcate" , "Describe accurately" , "Describe exactly" .)