Prisoners tense: row is building (12)
I believe the answer is:
construction
'is building' is the definition.
(thesaurus)
'prisoners tense row' is the wordplay.
'prisoners' becomes 'cons'.
'tense' becomes 't' (abbreviation used in many dictionaries).
'row' becomes 'ruction' (**).
'cons'+'t'+'ruction'='CONSTRUCTION'
(Other definitions for construction that I've seen before include "Process of erecting buildings" , "Act of building" , "Building; interpretation" , "Industry of erecting buildings" .)