Befoul, v. t. [imp. & p. p. Befouled; p. pr. & vb. n. Befouling.]
Etymology: [Cf. AS. bef; pref. be- + f to foul. See Foul, a.]
1. To make foul; to soil.
2. To entangle or run against so as to impede motion.
Shades of meaning
Fernald has no entry of its own for befoul; he lists it under defile.
He lists it without comment; the entries above explain its neighbors.