An endless labyrinth over large river (6)

I believe the answer is:

amazon

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'large river' is the definition.
'Amazon' can be an answer for 'river' (Amazon River is an example). I am unsure of the 'large' bit.

'an endless labyrinth over' is the wordplay.
'an' becomes 'a'.
'endless' means to remove the last letter.
'labyrinth' becomes 'maze' (synonyms).
'over' becomes 'on' (physically on top of).
'maze' with its final letter taken away is 'maz'.
'a'+'maz'+'on'='AMAZON'

Can you help me to learn more?

(Other definitions for amazon that I've seen before include "Fighting woman from a great river" , "Strong, well-built woman" , "Great river of S America, or a tough woman" , "Strong woman - large river" , "Mythic woman warrior" .)

I've seen this clue in the Evening Standard.

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