Function of Civil Service stopped by nothing (3)
I believe the answer is:
cos
'function' is the definition.
(mathematical function)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for cos that I've seen before include "Function briefly" , "Greek island (alternative spelling): Trig abbrev!" , "Senior officers" , "Salad plant" , "naturally having longer leaves than most" .)