American lawyer volunteers information (4)
I believe the answer is:
data
'information' is the definition.
(thesaurus)
'american lawyer volunteers' is the wordplay.
'american lawyer' becomes 'da' (abbreviation for District Attorney).
'volunteers' becomes 'ta' (abbreviation for Territorial Army).
'da'+'ta'='DATA'
(Other definitions for data that I've seen before include "Pieces of information" , "information from bank" , "Known facts" , "Facts and figures as processed by computer" , "Listed facts" .)