Take circuitous routes north of river (7)
I believe the answer is:
trouser
'river' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'take circuitous routes north of' is the wordplay.
'take' becomes 'r' (abbreviation for 'recipe', Latin for 'take').
'circuitous' indicates anagramming the letters.
'north of' says to put letters next to each other (in a down clue, some letters go above others).
'routes' with letters rearranged gives 'trouse'.
'r' put after 'trouse' is 'TROUSER'.
Can you help me to learn more?
(Other definitions for trouser that I've seen before include "Appropriate" , "For oneself" , "Pocket (something)" , "Our rest (anag)" , "Pocket (slang)" .)