Betting tapered off in use of radar (5,4)
I believe the answer is:
speed trap
'use of radar' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'betting tapered off in' is the wordplay.
'betting' becomes 'sp'.
'off' is an anagram indicator.
'in' means one lot of letters goes inside another.
'tapered' is an anagram of 'peedtra'.
'sp' enclosing 'peedtra' is 'SPEED TRAP'.
Can you help me to learn more?
(Other definitions for speed trap that I've seen before include "police operation" , "Hazard for fast motorist" , "that slows motorist?" , "curse of drivers?" , "Police control" .)