Crossword Genius

Unusual tea leaving baby with gas (4)

Ross

I believe the answer is:

neon

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

I cannot understand how the remainder of the clue works.

(Other definitions for neon that I've seen before include "Colourless gas, used in lighting" , "Brightly coloured advertising sign" , "Gas used in fluorescent lighting" , "Colourless, odourless rare gas" , "illuminating agent" .)

I've seen this clue in The Guardian.
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