Senior of two European articles (5)

I believe the answer is:

elder

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'senior' is the definition.
(I know that senior can be written as elder)

I don't understand the remainder of the clue.

(Other definitions for elder that I've seen before include "Tribal leader; tree" , "Senior - church official" , "White-flowered tree" , "Tree; of greater age" , "First-born" .)

I've seen this clue in The Guardian.

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