Source : Webster's Revised Unabridged Dictionary (1913)

Dull \Dull\, v. i.
   To become dull or stupid. --Rom. of R.

Dull \Dull\, a. [Compar. {Duller}; superl. {Dullest}.] [AS. dol
   foolish; akin to gedwelan to err, D. dol mad, dwalen to
   wander, err, G. toll mad, Goth. dwals foolish, stupid, cf.
   Gr. ? turbid, troubled, Skr. dhvr to cause to fall. Cf.
   {Dolt}, {Dwale}, {Dwell}, {Fraud}.]
   1. Slow of understanding; wanting readiness of apprehension;
      stupid; doltish; blockish. ``Dull at classical learning.''
      --Thackeray.

            She is not bred so dull but she can learn. --Shak.

   2. Slow in action; sluggish; unready; awkward.

            This people's heart is waxed gross, and their ears
            are dull of hearing.                  --Matt. xiii.
                                                  15.

            O, help my weak wit and sharpen my dull tongue.
                                                  --Spenser.

   3. Insensible; unfeeling.

            Think me not So dull a devil to forget the loss Of
            such a matchless wife.                -- Beau. & Fl.

   4. Not keen in edge or point; lacking sharpness; blunt. ``Thy
      scythe is dull.'' --Herbert.

   5. Not bright or clear to the eye; wanting in liveliness of
      color or luster; not vivid; obscure; dim; as, a dull fire
      or lamp; a dull red or yellow; a dull mirror.

   6. Heavy; gross; cloggy; insensible; spiritless; lifeless;
      inert. ``The dull earth.'' --Shak.

            As turning the logs will make a dull fire burn, so
            changes of study a dull brain.        -- Longfellow.

   7. Furnishing little delight, spirit, or variety;
      uninteresting; tedious; cheerless; gloomy; melancholy;
      depressing; as, a dull story or sermon; a dull occupation
      or period; hence, cloudy; overcast; as, a dull day.

            Along life's dullest, dreariest walk. -- Keble.

   Syn: Lifeless; inanimate; dead; stupid; doltish; heavy;
        sluggish; sleepy; drowsy; gross; cheerless; tedious;
        irksome; dismal; dreary; clouded; tarnished; obtuse. See
        {Lifeless}.

Dull \Dull\, v. t. [imp. & p. p. {Duller}; p. pr. & vb. n.
   {Dulling}.]
   1. To deprive of sharpness of edge or point. ``This . . .
      dulled their swords.'' --Bacon.

            Borrowing dulls the edge of husbandry. --Shak.

   2. To make dull, stupid, or sluggish; to stupefy, as the
      senses, the feelings, the perceptions, and the like.

            Those [drugs] she has Will stupefy and dull the
            sense a while.                        --Shak.

            Use and custom have so dulled our eyes. --Trench.

   3. To render dim or obscure; to sully; to tarnish. ``Dulls
      the mirror.'' --Bacon.

   4. To deprive of liveliness or activity; to render heavy; to
      make inert; to depress; to weary; to sadden.

            Attention of mind . . . wasted or dulled through
            continuance.                          --Hooker.

Source : WordNet®

dull
     adj 1: lacking in liveliness or animation; "he was so dull at
            parties"; "a dull political campaign"; "a large dull
            impassive man"; "dull days with nothing to do"; "how
            dull and dreary the world is"; "fell back into one of
            her dull moods" [ant: {lively}]
     2: emitting or reflecting very little light; "a dull glow";
        "dull silver badly in need of a polish"; "a dull sky"
        [ant: {bright}]
     3: being or made softer or less loud or clear; "the dull boom
        of distant breaking waves"; "muffled drums"; "the muffled
        noises of the street"; "muted trumpets" [syn: {muffled}, {muted},
         {softened}]
     4: so lacking in interest as to cause mental weariness; "a
        boring evening with uninteresting people"; "the deadening
        effect of some routine tasks"; "a dull play"; "his
        competent but dull performance"; "a ho-hum speaker who
        couldn't capture their attention"; "what an irksome task
        the writing of long letters is"- Edmund Burke; "tedious
        days on the train"; "the tiresome chirping of a cricket"-
        Mark Twain; "other people's dreams are dreadfully
        wearisome" [syn: {boring}, {deadening}, {ho-hum}, {irksome},
         {slow}, {tedious}, {tiresome}, {wearisome}]
     5: (of color) very low in saturation; highly diluted; "dull
        greens and blues"
     6: not keenly felt; "a dull throbbing"; "dull pain" [ant: {sharp}]
     7: slow to learn or understand; lacking intellectual acuity;
        "so dense he never understands anything I say to him";
        "never met anyone quite so dim"; "although dull at
        classical learning, at mathematics he was uncommonly
        quick"- Thackeray; "dumb officials make some really dumb
        decisions"; "he was either normally stupid or being
        deliberately obtuse"; "worked with the slow students"
        [syn: {dense}, {dim}, {dumb}, {obtuse}, {slow}]
     8: (of business) not active or brisk; "business is dull (or
        slow)"; "a sluggish market" [syn: {slow}, {sluggish}]
     9: not having a sharp edge or point; "the knife was too dull to
        be of any use" [ant: {sharp}]
     10: blunted in responsiveness or sensibility; "a dull gaze"; "so
         exhausted she was dull to what went on about her"- Willa
         Cather
     11: not clear and resonant; sounding as if striking with or
         against something relatively soft; "the dull thud";
         "thudding bullets" [syn: {thudding}]
     12: darkened with overcast; "a dark day"; "a dull sky"; "a gray
         rainy afternoon"; "gray clouds"; "the sky was leaden and
         thick" [syn: {gray}, {grey}, {leaden}]

dull
     v 1: make dull in appearance; "Age had dulled the surface"
     2: become dull or lusterless in appearance; lose shine or
        brightness; "the varnished table top dulled with time"
     3: deaden (a sound or noise), especially by wrapping [syn: {muffle},
         {mute}, {damp}, {dampen}, {tone down}]
     4: make numb or insensitive; "The shock numbed her senses"
        [syn: {numb}, {benumb}, {blunt}]
     5: make dull or blunt; "Too much cutting dulls the knife's
        edge" [syn: {blunt}] [ant: {sharpen}]
     6: become less interesting or attractive [syn: {pall}]
     7: make less lively or vigorous; "Middle age dulled her
        appetite for travel"