Source : Webster's Revised Unabridged Dictionary (1913)

Dreadful \Dread"ful\, a.
   1. Full of dread or terror; fearful. [Obs.] ``With dreadful
      heart.'' --Chaucer.

   2. Inspiring dread; impressing great fear; fearful; terrible;
      as, a dreadful storm. `` Dreadful gloom.'' --Milton.

            For all things are less dreadful than they seem.
                                                  --Wordsworth.

   3. Inspiring awe or reverence; awful. [Obs.] ``God's dreadful
      law.'' --Shak.

   Syn: Fearful; frightful; terrific; terrible; horrible;
        horrid; formidable; tremendous; awful; venerable. See
        {Frightful}.

Source : WordNet®

dreadful
     adj 1: causing fear or dread or terror; "the awful war"; "an awful
            risk"; "dire news"; "a career or vengeance so direful
            that London was shocked"; "the dread presence of the
            headmaster"; "polio is no longer the dreaded disease
            it once was"; "a dreadful storm"; "a fearful howling";
            "horrendous explosions shook the city"; "a terrible
            curse" [syn: {awful}, {dire}, {direful}, {dread(a)}, {dreaded},
             {fearful}, {fearsome}, {frightening}, {horrendous}, {horrific},
             {terrible}]
     2: exceptionally bad or displeasing; "atrocious taste";
        "abominable workmanship"; "an awful voice"; "dreadful
        manners"; "a painful performance"; "terrible handwriting";
        "an unspeakable odor came sweeping into the room" [syn: {atrocious},
         {abominable}, {awful}, {painful}, {terrible}, {unspeakable}]
     3: very unpleasant