Attorney volunteers information (4)
I believe the answer is:
data
'information' is the definition.
(data are bits of information)
'attorney volunteers' is the wordplay.
'attorney' becomes 'DA' (District Attorney).
'volunteers' becomes 'TA' (abbreviation for Territorial Army).
'da'+'ta'='DATA'
(Other definitions for data that I've seen before include "Gathered stats" , "What's stored by computers" , "Collected information" , "computer input?" , "Listed facts" .)