The Collaborative International Dictionary of English v.0.48:

Bitter \Bit"ter\, n. [See Bitts.] (Naut.)
   AA turn of the cable which is round the bitts.
   [1913 Webster]

   Bitter end, that part of a cable which is abaft the bitts,
      and so within board, when the ship rides at anchor.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bitter \Bit"ter\, a. [AS. biter; akin to Goth. baitrs, Icel.
   bitr, Dan., Sw., D., & G. bitter, OS. bittar, fr. root of E.
   bite. See Bite, v. t.]
   1. Having a peculiar, acrid, biting taste, like that of
      wormwood or an infusion of hops; as, a bitter medicine;
      bitter as aloes.
      [1913 Webster]

   2. Causing pain or smart; piercing; painful; sharp; severe;
      as, a bitter cold day.
      [1913 Webster]

   3. Causing, or fitted to cause, pain or distress to the mind;
      calamitous; poignant.
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            It is an evil thing and bitter, that thou hast
            forsaken the Lord thy God.            --Jer. ii. 19.
      [1913 Webster]

   4. Characterized by sharpness, severity, or cruelty; harsh;
      stern; virulent; as, bitter reproach.
      [1913 Webster]

            Husbands, love your wives, and be not bitter against
            them.                                 --Col. iii.
                                                  19.
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   5. Mournful; sad; distressing; painful; pitiable.
      [1913 Webster]

            The Egyptians . . . made their lives bitter with
            hard bondage.                         --Ex. i. 14.
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   Bitter apple, Bitter cucumber, Bitter gourd. (Bot.) See
      Colocynth.

   Bitter cress (Bot.), a plant of the genus Cardamine, esp.
      Cardamine amara.

   Bitter earth (Min.), tale earth; calcined magnesia.

   Bitter principles (Chem.), a class of substances, extracted
      from vegetable products, having strong bitter taste but
      with no sharply defined chemical characteristics.

   Bitter salt, Epsom salts; magnesium sulphate.

   Bitter vetch (Bot.), a name given to two European
      leguminous herbs, Vicia Orobus and Ervum Ervilia.

   To the bitter end, to the last extremity, however
      calamitous.
      [1913 Webster]

   Syn: Acrid; sharp; harsh; pungent; stinging; cutting; severe;
        acrimonious.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bitter \Bit"ter\, n.
   Any substance that is bitter. See Bitters.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bitter \Bit"ter\, v. t.
   To make bitter. --Wolcott.
   [1913 Webster]

WordNet (r) 3.0 (2006):

bitter
    adv 1: extremely and sharply; "it was bitterly cold"; "bitter
           cold" [syn: piercingly, bitterly, bitingly,
           bitter]
    adj 1: marked by strong resentment or cynicism; "an acrimonious
           dispute"; "bitter about the divorce" [syn: acrimonious,
           bitter]
    2: very difficult to accept or bear; "the bitter truth"; "a
       bitter sorrow"
    3: harsh or corrosive in tone; "an acerbic tone piercing
       otherwise flowery prose"; "a barrage of acid comments"; "her
       acrid remarks make her many enemies"; "bitter words";
       "blistering criticism"; "caustic jokes about political
       assassination, talk-show hosts and medical ethics"; "a
       sulfurous denunciation"; "a vitriolic critique" [syn:
       acerb, acerbic, acid, acrid, bitter, blistering,
       caustic, sulfurous, sulphurous, virulent,
       vitriolic]
    4: expressive of severe grief or regret; "shed bitter tears"
    5: proceeding from or exhibiting great hostility or animosity;
       "a bitter struggle"; "bitter enemies"
    6: causing a sharp and acrid taste experience;"quinine is
       bitter"
    7: causing a sharply painful or stinging sensation; used
       especially of cold; "bitter cold"; "a biting wind" [syn:
       biting, bitter]
    n 1: English term for a dry sharp-tasting ale with strong flavor
         of hops (usually on draft)
    2: the taste experience when quinine or coffee is taken into the
       mouth [syn: bitter, bitterness]
    3: the property of having a harsh unpleasant taste [syn:
       bitterness, bitter]
    v 1: make bitter

Moby Thesaurus II by Grady Ward, 1.0:

229 Moby Thesaurus words for "bitter":
   Siberian, acerb, acerbate, acerbic, acid, acidic, acidulent,
   acidulous, acrid, acrimonious, affecting, afflictive, aftertaste,
   algid, alienated, amaroidal, annoying, antagonistic, antipathetic,
   arctic, asperous, astringent, austere, bad, belligerent,
   below zero, bilious, biting, bitter as gall, bitterly cold, bleak,
   boreal, brisk, brumal, brutal, burning, caustic, cheerless,
   choleric, clashing, coarse, cold, cold as charity, cold as death,
   cold as ice, cold as marble, colliding, comfortless, conflicting,
   corroding, corrosive, crisp, cruel, cutting, deplorable,
   depressing, depressive, despiteful, disagreeable, discomforting,
   dislikable, dismal, dismaying, dispiriting, displeasing,
   distasteful, distressful, distressing, disturbing, divided,
   dolorific, dolorogenic, dolorous, double-edged, dreary, dyspeptic,
   edged, embittered, escharotic, estranged, fierce, flavor, freezing,
   freezing cold, frigid, full of hate, galling, gelid, glacial,
   grievous, gust, hard, harsh, hateful, hibernal, hiemal, hostile,
   hyperborean, ice-cold, ice-encrusted, icelike, icy, incisive,
   inclement, intemperate, irreconcilable, irritating, jaundiced,
   joyless, keen, lamentable, malevolent, malicious, malignant,
   miserable, mordacious, mordant, mournful, moving, nasty, nipping,
   nippy, nose-tickling, numbing, obnoxious, offensive, painful,
   palate, pathetic, penetrating, piercing, pinching, piquant,
   piteous, pitiable, poignant, provoking, pungent, quarrelsome,
   rancorous, rankled, raw, regrettable, relish, reproachful,
   repugnant, resentful, resenting, rigorous, rough, rueful, rugged,
   sad, saddening, salt, sapidity, sapor, savor, savoriness, scathing,
   scorching, set against, severe, sharp, sleety, slushy, smack,
   snappy, sore, sorrowful, sour, sour-tempered, soured, spiteful,
   splenetic, stabbing, stewing, stinging, stomach, stone-cold,
   strident, stringent, subzero, supercooled, sweet, tang, tart,
   taste, thankless, tongue, tooth, touching, trenchant, ugly,
   unalluring, unappealing, unappetizing, unattractive, uncomfortable,
   undelectable, undelicious, undesirable, unengaging, unenjoyable,
   uninviting, unkind, unlikable, unpalatable, unpleasant, unpleasing,
   unsavory, untasteful, unwelcome, vehement, venomous, vexatious,
   vicious, vinegarish, violent, virulent, vitriolic, winterbound,
   winterlike, wintery, wintry, withering, woebegone, woeful,
   wretched



Easton's 1897 Bible Dictionary:

Bitter
   Bitterness is symbolical of affliction, misery, and servitude
   (Ex. 1:14; Ruth 1:20; Jer. 9:15). The Chaldeans are called the
   "bitter and hasty nation" (Hab. 1:6). The "gall of bitterness"
   expresses a state of great wickedness (Acts 8:23). A "root of
   bitterness" is a wicked person or a dangerous sin (Heb. 12:15).

     The Passover was to be eaten with "bitter herbs" (Ex. 12:8;
   Num. 9:11). The kind of herbs so designated is not known.
   Probably they were any bitter herbs obtainable at the place and
   time when the Passover was celebrated. They represented the
   severity of the servitude under which the people groaned; and
   have been regarded also as typical of the sufferings of Christ.