Glass, one dropping to the floor? (7)
I believe the answer is:
tumbler
I believe this is a double definition.
'glass' is the first definition.
(tumbler is a kind of glass)
'one dropping to the floor?' is the second definition.
(someone who tumbles over)
(Other definitions for tumbler that I've seen before include "One flips" , "Drinking glass or old acrobat" , "Constantly dropping" , "Type of drinking glass" , "might be full of drink" .)