Suggest swallowing a large glass (7)
I believe the answer is:
opaline
'glass' is the definition.
(I've seen this before)
'suggest swallowing a large' is the wordplay.
'suggest' becomes 'opine' (I've seen this before**).
'swallowing' means one lot of letters goes inside another.
'large' becomes 'l'.
'a'+'l'='al'
'opine' placed around 'al' is 'OPALINE'.
(Other definitions for opaline that I've seen before include "milky" , "Photographic plate" , "Milk glass" , "whitish glass" , "Translucent glass" .)