The Collaborative International Dictionary of English v.0.48:

directional \directional\ adj.
   1. of or pertaining to direction (definition 2).
      [WordNet 1.5]

   2. serving to indicate direction.
      [PJC]

   3. (Radio) transmitting radio signals in a specific
      direction, or receiving signals only from a narrow angle
      of directions, thus serving to indicate the direction from
      which radio signals are coming. Used of antennas; as, a
      directional antenna.
      [PJC]

WordNet (r) 3.0 (2006):

directional
    adj 1: relating to or indicating directions in space; "a
           directional microphone" [ant: omnidirectional]
    2: relating to direction toward a (nonspatial) goal; "he tried
       to explain the directional trends of modern science"
    3: showing the way by conducting or leading; imposing direction
       on; "felt his mother's directing arm around him"; "the
       directional role of science on industrial progress" [syn:
       directing, directional, directive, guiding]