The Collaborative International Dictionary of English v.0.48:

Larrup \Lar"rup\, v. t. [imp. & p. p. Larruped; p. pr. & vb.
   n. Larruping.] [Perh, a corrupt. of lee rope, used by
   sailors in beating the boys; but cf. D. larpen to thresh,
   larp a whip, blow.]
   To beat or flog soundly. [Prov. Eng. & Colloq. U.S.] --Forby.
   [1913 Webster]

WordNet (r) 3.0 (2006):

larrup
    v 1: give a spanking to; subject to a spanking [syn: spank,
         paddle, larrup]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "larrup":
   bang, baste, batter, beat, buffet, clobber, dress down, drub, dust,
   flagellate, flail, flap, flax, flog, give a dressing-down, hammer,
   hide, knock, lambaste, lash, lather, leather, lick, maul, mop up,
   overwhelm, paddle, paste, patter, pelt, pommel, pound, pulverize,
   pummel, rap, scourge, shellac, sledgehammer, spank, stripe, tan,
   thrash, thresh, thump, trim, wallop, welt, whale, whip