The Collaborative International Dictionary of English v.0.48:

Ultima \Ul"ti*ma\ ([u^]l"i[i^]*m[.a]), a. [L., fem. of ultimus
   last.]
   Most remote; furthest; final; last.
   [1913 Webster]

   Ultima ratio [L.], the last reason or argument; the last
      resort.

   Ultima Thule. [L.] See Thule.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ultima Thule
    n 1: the geographical region believed by ancient geographers to
         be the northernmost land in the inhabited world [syn:
         Thule, ultima Thule]