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 ]
n. the property of a microphone or antenna of being more sensitive to signal arriving from one direction than from another. Syn. -- directivity. [ WordNet 1.5 ]