Ultima ratio

from 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]