uni·di·rec·tion·al /ˌjunɪdəˈrɛkʃnəl, daɪ, ʃənḷ/
  單向
  uni·di·rec·tion·al /ˌjunɪdəˈrɛkʃnəl, daɪ, ʃənḷ/ 形容詞
  unidirectional
  單向的
  unidirectional
       adj : operating or moving or allowing movement in one direction
             only; "a unidirectional flow"; "a unidirectional
             antenna"; "a unidirectional approach to a problem"
             [ant: bidirectional]