The Collaborative International Dictionary of English v.0.48:

Mountaineer \Moun`tain*eer"\ (moun`t[i^]n*[=e]r"), n. [OF.
   montanier, LL. montanarius. See Mountain.]
   1. An inhabitant of a mountain; one who lives among
      mountains.
      [1913 Webster]

   2. A rude, fierce person. [Obs.]
      [1913 Webster]

            No savage fierce, bandit, or mountaineer. --Milton.
      [1913 Webster]

   3. A person who climbs mountains for sport.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

mountaineer \moun`tain*eer"\, v. i.
   To live or act as a mountaineer; to climb mountains.
   [1913 Webster]

         You can't go mountaineering in a flat country. --H.
                                                  James.
   [1913 Webster]

WordNet (r) 3.0 (2006):

mountaineer
    n 1: someone who climbs mountains [syn: mountaineer, mountain
         climber]
    v 1: climb mountains for pleasure as a sport