Daughter’s joining a corporation in fact (5)
I believe the answer is:
datum
'fact' is the definition.
(thesaurus)
'daughter's joining a corporation' is the wordplay.
'daughter' becomes 'd'.
'joining' is a charade indicator (letters next to each other).
'corporation' becomes 'tum' (I've seen this before).
'd'+'a'+'tum'='DATUM'
'in' is the link.
(Other definitions for datum that I've seen before include "Minimal information" , "Single informative fact" , "Given piece of information" , "Premiss, thing taken for granted" , "Given point or position" .)