Crossword Genius

Gall as old Greek character almost drowned in beer (3,5)

Ross

I believe the answer is:

oak apple

'gall' is the definition.
(I know that Oak apple is a gall)

I cannot understand how the rest of the clue works.

(Other definitions for oak apple that I've seen before include "Charles II's day?" , "Gall on tree containing wasp larvae" , "restoring the monarchy on this day!" , "growth made by wasp" , "Gall on some trees" .)

I've seen this clue in The Guardian.
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