The Collaborative International Dictionary of English v.0.48:
Afoul \A*foul"\, adv. & a. [Pref. a- + foul.] In collision; entangled. --Totten. [1913 Webster] To run afoul of, to run against or come into collision with, especially so as to become entangled or to cause injury. [1913 Webster]WordNet (r) 3.0 (2006):
afoul adj 1: especially of a ship's lines etc; "with its sails afoul"; "a foul anchor" [syn: afoul(ip), foul, fouled]