The Collaborative International Dictionary of English v.0.48:

Bemoil \Be*moil"\, v. t. [Pref. be- + moil, fr. F. mouiller to
   wet; but cf. also OE. bimolen to soil, fr. AS. m[=a]l spot:
   cf. E. mole.]
   To soil or encumber with mire and dirt. [Obs.] --Shak.
   [1913 Webster]