DICT.TW Dictionary Taiwan

 steep·en /ˈstipən, pṃ/
 (vt.)使陡峭(vi.)變陡峭

 Steep·en v. i. [imp. & p. p. Steepened p. pr. & vb. n. Steepening.] To become steep or steeper.
    As the way steepened . . . I could detect in the hollow of the hill some traces of the old path.   --H. Miller.
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 steepen
      v 1: become steeper; "The mountain side has steepened"
      2: make steeper; "The landslides have steepened the mountain
         sides"