Indefinite number on street work incessantly (3-4)
I believe the answer is:
non-stop
'incessantly' is the definition.
Both the definition and answer are adverbs. Maybe there's an association between them I don't understand?
'indefinite number on street work' is the wordplay.
'indefinite number' becomes 'n' (n can represent any number).
'street' becomes 'st' (abbreviation).
'work' becomes 'op' (abbreviation for opus).
'n'+'on'+'st'+'op'='NON-STOP'
Can you help me to learn more?
(Other definitions for non-stop that I've seen before include "Round-the-clock" , "Unceasing" , "Going straight from A to B" , "Continuous" , "Ceaseless" .)