One travelling down Amazon, perhaps (6)
I believe the answer is:
driver
'one travelling' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'down amazon perhaps' is the wordplay.
'down' becomes 'd'.
'amazon perhaps' becomes 'river' (amazon is a kind of river).
'd'+'river'='DRIVER'
Can you help me to learn more?
(Other definitions for driver that I've seen before include "chauffeuse" , "Operator of a motor vehicle" , "Member of RAC" , "Flat-faced golf club" , "Motorist - golf club" .)