Unoccupied, like a milk bottle (5)
I believe the answer is:
empty
This might be a double definition.
'unoccupied' is the first definition.
(similar in meaning)
'milk bottle' is the second definition.
'empty' can be an answer for 'milk' (thesaurus). I'm not certain of the 'bottle' bit.
'like a' acts as a link.
Can you help me to learn more?
(Other definitions for empty that I've seen before include "worthless" , "Free" , "Arabic quarter" , "left for the milkman?" , "Dead man" .)