Acrobat's glass (7)
I believe the answer is:
tumbler
This clue is a double definition.
'acrobat's' is the first definition.
(synonyms)
'glass' is the second definition.
(I know that Tumbler is a glass)
(Other definitions for tumbler that I've seen before include "Type of drinking glass" , "vessel" , "slipper may become this" , "One repeatedly turning over" , "Constantly dropping" .)