Crossword Genius

Toast and two-thirds of Stilton, perhaps with port (7)

Ross

I believe the answer is:

cheerio

'toast' is the definition.
(I've seen this before)

I don't understand how the rest of the clue works.

(Other definitions for cheerio that I've seen before include "Farewell - drinking toast" , "An informal hearty goodbye" , "Ta-ta" , "Say this before drinking" , "Expression used when leaving" .)

I've seen this clue in The Times.
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