A corporation beyond despicable at first — fact! (5)
I believe the answer is:
datum
'fact' is the definition.
(thesaurus)
'a corporation beyond despicable at first' is the wordplay.
'corporation' becomes 'tum' (I've seen this before).
'beyond' says to put letters next to each other.
'at first' indicates taking the first letters.
The first letter of 'despicable' is 'd'.
'a'+'tum'='atum'
'atum' after 'd' is 'DATUM'.
(Other definitions for datum that I've seen before include "bit of info" , "Something given" , "Bit of dope" , "One item of information" , "Single informative fact" .)