It was a habit in Ancient Rome (4)
I believe the answer is:
toga
'habit in ancient rome' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'it was a' is the wordplay.
'it' becomes ''t' (abbreviation. e.g. in 'tis).
'was' becomes 'og' (I can't justify this - if you can you should give a lot more credence to this answer).
't'+'og'+'a'='TOGA'
Can you help me to learn more?
(Other definitions for toga that I've seen before include "Outer garment" , "This ancient robe might get your goat" , "Robe of ancient Rome" , "Cloak of ancient Rome" , "Got a robe for an old Roman" .)