Crossword Genius

Things of no importance in glass? (5,4)

Ross

I believe the answer is:

small beer

I'm a little stuck... Click here to teach me more about this clue!

This might be a double definition.

'things of no importance' is the first definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

'glass?' is the second definition.
(I've seen this before)

'in' acts as a link.

Can you help me to learn more?

(Other definitions for small beer that I've seen before include "People or things of no importance" , "Half, perhaps" , "no significance" , "trivial stuff" , "Half, say" .)

I've seen this clue in The Telegraph.
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