Debauchery enters city, over time (4)
I believe the answer is:
riot
'debauchery' is the definition.
(I know that debauchery can be written as riot)
'city over time' is the wordplay.
'city' becomes 'rio' (Rio de Janeiro).
'over' says to put letters next to each other (in a down clue, some letters go over others).
'time' becomes 't' (abbreviation).
'rio'+'t'='RIOT'
'enters' is the link.
This may not be right. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for riot that I've seen before include "scream" , "Affray, fighting in the streets" , "Take to the streets" , "Violent disturbance by mob" , "Uproar" .)