Gas one twice bottles? (4)
I believe the answer is:
neon
'gas' is the definition.
(I've seen this before)
'one twice bottles?' is the wordplay.
'one twice' means two substitutions for 'one'.
'bottles?' indicates the answer is hidden within the clue (bottling is a kind of containing).
'NEON' can be found hidden inside 'one one'.
(Other definitions for neon that I've seen before include "Type of lighting" , "Gaseous element, in advertising signs, say" , "Gas used in fluorescent lights" , "Could it brighten proceedings" , "Noble gas used in illuminated signs" .)