Crossword Genius

Oil suppliers spot south-east river rising (9)

Ross

I believe the answer is:

pipelines

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'oil suppliers' is the definition.
Although both the answer and definition are plural nouns, I don't understand how they can define each other.

'spot south-east river rising' is the wordplay.
'spot' becomes 'pip' (I've seen this before).
'south east' becomes 'se'.
'river' becomes 'nile' (Nile is an example**).
'rising' says the letters should be written backwards (going up in a down clue).
'se'+'nile'='senile'
'senile' in reverse letter order is 'elines'.
'pip'+'elines'='PIPELINES'

Can you help me to learn more?

I've seen this clue in The Times.
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