Lawyer volunteers information (4)
I believe the answer is:
data
'information' is the definition.
(thesaurus)
'lawyer volunteers' is the wordplay.
'lawyer' becomes 'da' (D.A. is an example).
'volunteers' becomes 'ta' (abbreviation for Territorial Army).
'da'+'ta'='DATA'
(Other definitions for data that I've seen before include "intelligence" , "What's stored by computers" , "Facts - Star Trek android" , "Raw facts" , "Series of measurements" .)