this is an interesting word, which probably gets different treatment from different resources. W3 gives cattywampus as a variant of catawamp[o]us, which in turn has two listings. the first is marked "dial. an imaginary fierce wild animal", probably an alteration of catamount. the second is your adjective, given as "1) fierce, savage 2) askew, awry, cater-cornered", probably by folk etymology [misapprehension] from catercorner. I'll check OED too, unless someone else has it.

p.s. - this also merits YART status (yet another rehashed topic)
http://wordsmith.org/board/showthreaded.pl?Cat=&Board=words&Number=3495