Odd-job man about to enter big old corporation (8)
I believe the answer is:
factotum
'odd-job man' is the definition.
(a factotum does multiple kinds of work)
'to enter big old corporation' is the wordplay.
'to enter big' becomes 'fact' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'old' becomes 'o' (abbreviation).
'corporation' becomes 'tum' (I've seen this before).
'fact'+'o'+'tum'='FACTOTUM'
'about' acts as a link.
Can you help me to learn more?
(Other definitions for factotum that I've seen before include "Person employed to do all sorts of work" , "junior official" , "Employee with a variety of jobs" , "Assistant doing all kinds of work" , "Versatile employee" .)