JEFFERSONIAN is a 12 letter word that starts with J.

1. \Jef`fer*so"ni*an\, a.
   Pertaining to, or characteristic of, Thomas Jefferson or his
   policy or political doctrines. --Lowell.
   
   

2. \Jef`fer*so"ni*an\, a.
   Pert. to, or characteristic of, Thomas Jefferson (third
   President of the United States) or his political doctrines,
   which were those of the Republicanism of his time, as opposed
   to those of the Federalists. -- n. An adherent of Jefferson
   or his doctrines. -- {Jef`fer*so"ni*an*ism}, n.