The Collaborative International Dictionary of English v.0.48:

Far \Far\, a. [Fartherand Farthestare used as the compar.
   and superl. of far, although they are corruptions arising
   from confusion with further and furthest. See Further.]
   [OE. fer, feor, AS. feor; akin to OS. fer, D. ver, OHG.
   ferro, adv., G. fern, a., Icel. fjarri, Dan. fjirn, Sw.
   fjerran, adv., Goth. fa[imac]rra, adv., Gr. ????? beyond,
   Skr. paras, adv., far, and prob. to L. per through, and E.
   prefix for-, as in forgive, and also to fare. Cf. Farther,
   Farthest.]
   1. Distant in any direction; not near; remote; mutually
      separated by a wide space or extent.
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            They said, . . . We be come from a far country.
                                                  --Josh. ix. 6.
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            The nations far and near contend in choice.
                                                  --Dryden.
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   2. Remote from purpose; contrary to design or wishes; as, far
      be it from me to justify cruelty.
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   3. Remote in affection or obedience; at a distance, morally
      or spiritually; t enmity with; alienated.
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            They that are far from thee ahsll perish. --Ps.
                                                  lxxiii. 27.
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   4. Widely different in nature or quality; opposite in
      character.
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            He was far from ill looking, though he thought
            himself still farther.                --F. Anstey.
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   5. The more distant of two; as, the far side (called also off
      side) of a horse, that is, the right side, or the one
      opposite to the rider when he mounts.
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   Note: The distinction between the adjectival and adverbial
         use of far is sometimes not easily discriminated.
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   By far, by much; by a great difference.

   Far between, with a long distance (of space or time)
      between; at long intervals. "The examinations are few and
      far between." --Farrar.
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The Collaborative International Dictionary of English v.0.48:

Farther \Far"ther\ (f[aum]r"[th][~e]r), a., compar. of Far.
   [superl. Farthest (-[th][e^]st). See Further.] [For
   farrer, OE. ferrer, compar. of far; confused with further.
   Cf. Farthest.]
   1. More remote; more distant than something else.
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   2. Tending to a greater distance; beyond a certain point;
      additional; further.
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            Before our farther way the fates allow. --Dryden.
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            Let me add a farther Truth.           --Dryden.
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            Some farther change awaits us.        --MIlton.
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The Collaborative International Dictionary of English v.0.48:

Farther \Far"ther\, adv.
   1. At or to a greater distance; more remotely; beyond; as,
      let us rest with what we have, without looking farther.
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   2. Moreover; by way of progress in treating a subject; as,
      farther, let us consider the probable event.
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   No farther, (used elliptically for) go no farther; say no
      more, etc.
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            It will be dangerous to go on. No farther ! --Shak.
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The Collaborative International Dictionary of English v.0.48:

Farther \Far"ther\, v. t.
   To help onward. [R.] See Further.
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WordNet (r) 3.0 (2006):

farther
    adv 1: to or at a greater extent or degree or a more advanced
           stage (`further' is used more often than `farther' in
           this abstract sense); "further complicated by uncertainty
           about the future"; "let's not discuss it further";
           "nothing could be further from the truth"; "they are
           further along in their research than we expected"; "the
           application of the law was extended farther"; "he is
           going no farther in his studies" [syn: further,
           farther]
    2: to or at a greater distance in time or space (`farther' is
       used more frequently than `further' in this physical sense);
       "farther north"; "moved farther away"; "farther down the
       corridor"; "the practice may go back still farther to the
       Druids"; "went only three miles further"; "further in the
       future" [syn: farther, further]
    adj 1: more distant in especially space or time; "they live in
           the farther house"
    2: more distant in especially degree; "nothing could be further
       from the truth"; "further from our expectations"; "farther
       from the truth"; "farther from our expectations" [syn:
       further, farther]

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "farther":
   above, accessory, added, additional, additionally, again,
   all included, also, altogether, among other things, ancillary,
   and all, and also, and so, another, as well, au reste, auxiliary,
   beside, besides, beyond, collateral, contributory, else, en plus,
   extra, for lagniappe, fresh, further, furthermore, in addition,
   inter alia, into the bargain, item, likewise, more, more distant,
   moreover, new, now, on the side, on top of, other, over, plus,
   remoter, similarly, spare, supernumerary, supplemental,
   supplementary, surplus, then, therewith, thither, to boot, too,
   ulterior, yet, yon, yonder