Adam Clarke on Isaiah 40:4

Crooked - The word עקב akob is very generally rendered crooked: but this sense of the word seems not to be supported by any good authority. Ludolphus, Comment. ad Hist. Aethiop. p. 206, says "that in the Ethiopia language it signifies clivus, locus editus:" and so the Syriac Version renders it in this place, ערמא arama: Hebrew, ערמה aramah, tumulus, acervus. Thus the parallelism would be more perfect:" the hilly country shall be made level, and the precipices a smooth plain."