An Etymological Dictionary of the German Language/steil
steil, adj., ‘steep,’ from the equiv. late the variants of which, steigel, OHG. steigal, prove the origin of steil (lit. ‘mounting’) from the cognates discussed under Steig. Comp. Du. steil, AS. stœ̂gl, stœ̂ger, ‘steep’; to these are allied OHG. stëcchal, stëhhal, MidHG. stëckel (stëchel), ‘steep,’ Bav., Alsat., MidHG., and LG. štickel, ‘steep’ (in the UpG. dialects steil seems to be entirely unknown).