Steepen

• (v. i.) To become steep or steeper.
Found on http://thinkexist.com/dictionary/meaning/steepen/

Steepen

Steep'en intransitive verb [ imperfect & past participle Steepened ; present participle & verbal noun Steepening .] To become steep or steeper. « As the way steepened . . . I could detect in the hollow of the hill some traces...
Found on http://www.encyclo.co.uk/webster/S/190

steepen

[v] - become steeper 2. [v] - make steeper
Found on http://www.webdictionary.co.uk/definition.php?query=steepen
No exact match found