Source : Webster's Revised Unabridged Dictionary (1913)

Sad \Sad\ (s[a^]d), a. [Compar. {Sadder}; supperl. {Saddest}.]
   [OE. sad sated, tired, satisfied, firm, steadfast, AS. s[ae]d
   satisfied, sated; akin to D. zat, OS. sad, G. satt, OHG. sat,
   Icel. sa[eth]r, saddr, Goth. sa[thorn]s, Lith. sotus, L. sat,
   satis, enough, satur sated, Gr. 'a`menai to satiate, 'a`dnh
   enough. Cf. {Assets}, {Sate}, {Satiate}, {Satisfy},
   {Satire}.]
   1. Sated; satisfied; weary; tired. [Obs.]

            Yet of that art they can not waxen sad, For unto
            them it is a bitter sweet.            --Chaucer.

   2. Heavy; weighty; ponderous; close; hard. [Obs., except in a
      few phrases; as, sad bread.]

            His hand, more sad than lump of lead. --Spenser.

            Chalky lands are naturally cold and sad. --Mortimer.

   3. Dull; grave; dark; somber; -- said of colors.
      ``Sad-colored clothes.'' --Walton.

            Woad, or wade, is used by the dyers to lay the
            foundation of all sad colors.         --Mortimer.

   4. Serious; grave; sober; steadfast; not light or frivolous.
      [Obs.] ``Ripe and sad courage.'' --Chaucer.

            Lady Catharine, a sad and religious woman. --Bacon.

            Which treaty was wisely handled by sad and discrete
            counsel of both parties.              --Ld. Berners.

   5. Affected with grief or unhappiness; cast down with
      affliction; downcast; gloomy; mournful.

            First were we sad, fearing you would not come; Now
            sadder, that you come so unprovided.  --Shak.

            The angelic guards ascended, mute and sad. --Milton.

   6. Afflictive; calamitous; causing sorrow; as, a sad
      accident; a sad misfortune.

   7. Hence, bad; naughty; troublesome; wicked. [Colloq.] ``Sad
      tipsy fellows, both of them.'' --I. Taylor.

   Note: Sad is sometimes used in the formation of
         self-explaining compounds; as, sad-colored, sad-eyed,
         sad-hearted, sad-looking, and the like.

   {Sad bread}, heavy bread. [Scot. & Local, U.S.] --Bartlett.

   Syn: Sorrowful; mournful; gloomy; dejected; depressed;
        cheerless; downcast; sedate; serious; grave; grievous;
        afflictive; calamitous.

Sadder \Sad"der\, n.
   Same as {Sadda}.

Source : WordNet®

sad
     adj 1: experiencing or showing sorrow or unhappiness; "feeling sad
            because his dog had died"; "Better by far that you
            should forget and smile / Than that you should
            remember and be sad"- Christina Rossetti [ant: {glad}]
     2: of things that make you feel sad; "sad news"; "she doesn't
        like sad movies"; "it was a very sad story"; "When I am
        dead, my dearest, / Sing no sad songs for me"- Christina
        Rossetti
     3: bad; unfortunate; "my finances were in a deplorable state";
        "a lamentable decision"; "her clothes were in sad shape";
        "a sorry state of affairs" [syn: {deplorable}, {distressing},
         {lamentable}, {pitiful}, {sorry}]
     [also: {saddest}, {sadder}]

sadder
     See {sad}