Seasonal worker police force brought onto firm (5)
I believe the answer is:
comet
'seasonal worker police' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'force brought onto firm' is the wordplay.
I cannot really see how this works, but
'force' could be 'met' (I've seen this in other clues) and 'met' is found within the answer.
'firm' could be 'co' (a firm is a company) and 'co' is found within the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for comet that I've seen before include "Dancer's colleague" , "Orbiting extraterrestrial body" , "Small orbiting body in the solar system" , "Object in space with bright centre and long hazy tail" , "Omen supposedly" .)