The Collaborative International Dictionary of English v.0.48:

Dominus \Dom"i*nus\, n.; pl. Domini. [L., master. See Dame.]
   Master; sir; -- a title of respect formerly applied to a
   knight or a clergyman, and sometimes to the lord of a manor.
   --Cowell.
   [1913 Webster]

WordNet (r) 3.0 (2006):

dominus
    n 1: a clergyman; especially a settled minister or parson [syn:
         dominus, dominie, domine, dominee]