River one could label American? (5)

I believe the answer is:

tagus

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'river' is the definition.
(Tagus River is an example)

'label american?' is the wordplay.
'label' becomes 'tag' (tag is a kind of label).
'american?' becomes 'US' (abbreviation for United States).
'tag'+'us'='TAGUS'

'one could' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.

Can you help me to learn more?

(Other definitions for tagus that I've seen before include "River of Spain and Portugal" , "waterway" , "Longest river of Iberian peninsular" , "Current" , "Lisbon's river" .)

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