Steepen \Steep"en\ (st[=e]p"'n), v. i. [imp. & p. p. {Steepened}
(st[=e]p"'nd); p. pr. & vb. n. {Steepening}.]
To become steep or steeper.
[1913 Webster]
As the way steepened . . . I could detect in the hollow
of the hill some traces of the old path. --H. Miller.
[1913 Webster]