Fact corporation presented to US lawyer (5)
I believe the answer is:
datum
'fact' is the definition.
(thesaurus)
'corporation presented to us lawyer' is the wordplay.
'corporation' becomes 'tum' (I've seen this before).
'presented to' means one lot of letters go next to another.
'us lawyer' becomes 'da' (abbreviation for District Attorney).
'tum' put after 'da' is 'DATUM'.
(Other definitions for datum that I've seen before include "Given piece of information" , "Something given" , "Little bit of information" , "Fixed starting point for measurements" , "Single informative fact" .)