Joins as senior on board (7)

I believe the answer is:

solders

'joins' is the definition.
(soldering is a kind of joining)

'senior on board' is the wordplay.
'senior' becomes 'older' (synonyms).
'on' means one lot of letters goes inside another.
'board' becomes 'ss' (I've seen this in other clues).
'older' going within 'ss' is 'SOLDERS'.

'as' acts as a link.

(Another definition for solders that I've seen is " Joins".)

I've seen this clue in The Globe and Mail.

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