Definition of rhaetian:
(n) :
A native or inhabitant of Rhaetia in central and eastern Switzerland.
(adj) :
Pertaining to the culture or geography of Raetia.
(n) :
(linguistics) An extinct non-Romance language spoken in the ancient region of Raetia in the eastern Alps in pre-Roman and Roman times.
(n) :
Rhaeto-Romance, a continuum of modern Romance languages spoken in much the same region.