The Collaborative International Dictionary of English v.0.48:

Lariat \Lar"i*at\ (l[a^]r"[i^]*[a^]t), v. t. [imp. & p. p.
   Lariated; p. pr. & vb. n. Lariating.]
   To secure with a lariat fastened to a stake, as a horse or
   mule for grazing; also, to lasso or catch with a lariat.
   [Western U.S.]
   [1913 Webster]