What wqould the Latin for “Lesser Citizen” or “Lesser Roman” be?
Plebs, plebis (f) for “the lower class”.
I dunno, but I know this belongs in GQ.
Perhaps you could go with something like civis minor.
Ah drat. I must have clicked on the wrong forum name. Sorry! 
From http://www.bible-history.com/rome/RomeRoman_Citizenship.htm:
From http://www.bible-history.com/rome/RomeRoman_Citizenship_Facts.htm: