Puzzle briefly referring to river (6)
I believe the answer is:
amazon
'river' is the definition.
(Amazon is an example)
'puzzle briefly referring to' is the wordplay.
'puzzle' becomes 'amaze' (both can mean to astound or confuse).
'briefly' means to remove the last letter.
'referring to' becomes 'on' (eg books on or referring to a certain topic).
'amaze' with its last letter taken away is 'amaz'.
'amaz'+'on'='AMAZON'
(Other definitions for amazon that I've seen before include "tropical fish swimming here" , "Mighty river of S America, or tough woman" , "One of a mythic nation of women warriors" , "Female warrior of Greek myth" , "running through Peru, Colombia and Brazil" .)