Job limits I assume to be valid (5)
I believe the answer is:
posit
'assume to be valid' is the definition.
I can't judge whether this definition defines the answer.
'job limits i' is the wordplay.
'job' becomes 'post' (post is a kind of job).
'limits' indicates putting letters inside (limit can mean to contain or block off).
'post' going around 'i' is 'POSIT'.
Can you help me to learn more?
(Other definitions for posit that I've seen before include "state" , "Propose" , "Put forward (argument)" , "Put forward (a theory)" , "Lay down or assume (as the basis for an argument)" .)