Vermin exterminator's second employer (6)
I believe the answer is:
mouser
'vermin exterminator's second employer' is the definition.
I can't judge whether this defines the answer.
'second employer' is the wordplay.
'second' becomes 'mo' (both are short periods of time).
'employer' becomes 'user' (someone who employs or uses something).
'mo'+'user'='MOUSER'
Can you help me to learn more?
(Other definitions for mouser that I've seen before include "Preying cat" , "moggy" , "Useful mog" , "Cat proficient at catching small rodents" , "pest controller" .)