Source : Webster's Revised Unabridged Dictionary (1913)

Regius \Re"gi*us\ (r?l"?*?s), a. [L. regius, from rex, regis, a
   king.]
   Of or pertaining to a king; royal.

   {Regius professor}, an incumbent of a professorship founded
      by royal bounty, as in an English university.

Source : WordNet®

Regius professor
     n : holder of a British professorship created by a royal patron