[1] : The Collaborative International Dictionary of English v.0.48

ultima \ul"tima\ u^l"ii^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
see also:
ultima ratio ultima thule thule 

[2] : The Collaborative International Dictionary of English v.0.48

ultima \ul"tima\, n. l., fem. of ultimus last. gram. 
   pros.
   the last syllable of a word.
   1913 webster

Ultima >> U Words
Ultima, definition of term: Ultima
ultima_pag1.html

Ultima Thule >> U Words
Ultima Thule, definition of term: Ultima Thule
ultima+thule_pag1.html