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

ultra- \ul"tra-\, a.
   a prefix from the latin ultra beyond see ulterior, having
   in composition the signification beyond, on the other side,
   chiefly when joined with words expressing relations of place;
   as, ultramarine, ultramontane, ultramundane, ultratropical,
   etc. in other relations it has the sense of excessively,
   exceedingly, beyond what is common, natural, right, or
   proper; as, ultraconservative; ultrademocratic,
   ultradespotic, ultraliberal, ultraradical, etc.
   1913 webster
see also:
ulterior 

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

ultra \ul"tra\, a. see ultra-.
   going beyond others, or beyond due limit; extreme; fanatical;
   uncompromising; as, an ultra reformer; ultra measures.
   1913 webster
see also:
ultra- 

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

ultra \ul"tra\, n.
   one who advocates extreme measures; an ultraist; an
   extremist; a radical. --brougham.
   1913 webster

[4] : WordNet (r) 2.0

ultra
     adj : used of opinions and actions far beyond the norm;
           "extremist political views"; "radical opinions on
           education"; "an ultra conservative" syn: extremist,
           radical
see also:
extremist radical 

[5] : Moby Thesaurus II by Grady Ward, 1.0

41 moby thesaurus words for "ultra":
   bolshevik, jacobin, wobbly, anarchist, anarcho-syndicalist,
   at the height, at the limit, extreme, extreme left-winger,
   extremist, fanatic, far out, furthest, greatest, kinky,
   left-wing extremist, lunatic fringe, mild radical, most, nihilist,
   outre, parlor bolshevik, parlor pink, pink, pinko, rabid, radical,
   red, revolutional, revolutionary, revolutionist, sans-culotte,
   subversive, syndicalist, too much, ultra-ultra, ultraist, utmost,
   uttermost, way out, yippie

Ultra >> U Words
Ultra, definition of term: Ultra
ultra_pag1.html

Ultra Vires >> U Words
Ultra Vires, definition of term: Ultra Vires
ultra+vires_pag1.html

Ne Plus Ultra >> N Words
Ne Plus Ultra, definition of term: Ne Plus Ultra
ne+plus+ultra_pag1.html