The Collaborative International Dictionary of English v.0.48:

Lather \Lath"er\ (l[a^][th]"[~e]r), n. [AS. le['a][eth]or niter,
   in le['a][eth]orwyrt soapwort; cf. Icel. lau[eth]r; perh.
   akin to E. lye.]
   1. Foam or froth made by soap moistened with water.
      [1913 Webster]

   2. Foam from profuse sweating, as of a horse.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Lather \Lath"er\, v. t. [imp. & p. p. Lathered
   (l[a^][th]"[~e]rd); p. pr. & vb. n. Lathering.] [AS.
   l[=e][eth]rian to lather, anoint. See Lather, n. ]
   To spread over with lather; as, to lather the face.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Lather \Lath"er\, v. i.
   To form lather, or a froth like lather; to accumulate foam
   from profuse sweating, as a horse.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Lather \Lath"er\, v. t. [Cf. Leather.]
   To beat severely with a thong, strap, or the like; to flog.
   [Low]
   [1913 Webster] Lathereeve

WordNet (r) 3.0 (2006):

lather
    n 1: the froth produced by soaps or detergents [syn: soapsuds,
         suds, lather]
    2: agitation resulting from active worry; "don't get in a stew";
       "he's in a sweat about exams" [syn: fret, stew, sweat,
       lather, swither]
    3: a workman who puts up laths
    4: the foam resulting from excessive sweating (as on a horse)
    v 1: beat severely with a whip or rod; "The teacher often
         flogged the students"; "The children were severely
         trounced" [syn: flog, welt, whip, lather, lash,
         slash, strap, trounce]
    2: form a lather; "The shaving cream lathered"
    3: exude sweat or lather; "this unfit horse lathers easily"
    4: rub soap all over, usually with the purpose of cleaning [syn:
       soap, lather]

Moby Thesaurus II by Grady Ward, 1.0:

171 Moby Thesaurus words for "lather":
   BO, aerate, anxiety, baptize, bath, bathe, beaded brow,
   beads of sweat, beat, beat all hollow, beat hollow, belabor, best,
   body odor, bother, breakers, breathless impatience, buffet, bustle,
   chafing, clamor, cold sweat, collar, cream, defeat, destroy,
   diaphoresis, disquietude, dither, do in, douche, dress down, drub,
   eagerness, excitement, exudate, exudation, fix, flagellate, flail,
   flap, flax, flog, flush, flush out, fluster, flusteration,
   flustration, flutter, foam, foofaraw, fret, fretfulness, fretting,
   froth, fuss, gargle, give a dressing-down, hassle, haste, head,
   hide, holystone, honest sweat, hors de combat, hubbub, impatience,
   impatientness, impetuousness, irrigate, lambaste, larrup, lash,
   launder, lave, leather, lick, mantle, maul, meringue, mop, mop up,
   mousse, offscum, outclass, outdo, outfight, outgeneral,
   outmaneuver, outpoint, outrun, outsail, outshine, paddle,
   perspiration, perspiration odor, pother, pucker, puff, pummel, put,
   restiveness, restlessness, rinse, rinse out, ritually immerse,
   ruin, scour, scrub, scrub up, scud, scum, sea foam, settle,
   shampoo, shower, skin, skin alive, sluice, sluice out, soap,
   soapsuds, souffle, spindrift, sponge, spoondrift, spray, spume,
   state, stew, stinging, streams of sweat, sud, sudor, sudoresis,
   suds, surf, swab, sweat, swelter, swivet, syringe, tan,
   tense readiness, thrash, tizzy, toivel, trim, triumph over,
   trounce, tub, turmoil, twitter, twitteration, undo, uneasiness,
   unpatientness, unquietness, wallop, wash, wash out, wash up, water,
   welt, whack, whale, whip, whisk, white water, worst, yeast