The Collaborative International Dictionary of English v.0.48:

Space walk \Space walk\, n.
   any activity by a human outside of the protective environment
   of a spacecraft while it is in outer space, requiring a space
   suit to protect the person from the vacuum and other hazards
   of space.
   [PJC]

WordNet (r) 3.0 (2006):

space walk
    n 1: any kind of physical activity outside a spacecraft by one
         of the crew

Moby Thesaurus II by Grady Ward, 1.0:

23 Moby Thesaurus words for "space walk":
   aerospace medicine, aerospace research, aerospace science,
   aerospace technology, astronautics, bioastronautics, break free,
   escape earth, escape velocity, go into orbit, grand tour,
   interplanetary travel, navigate in space, orbit the earth,
   park in space, rocketry, science fiction, shoot into space,
   space flight, space medicine, space travel, step flight,
   trip to Mars