Employer's cat second to be taken (4)
I believe the answer is:
user
'employer's' is the definition.
(someone who employs or uses something)
I cannot understand how the remainder of the clue works.
(Other definitions for user that I've seen before include "One operating something" , "Operator; exploiter" , "Person who takes drugs" , "One exploiting others" , "Manipulator" .)