Source : Webster's Revised Unabridged Dictionary (1913)

Grievous \Griev"ous\, a. [OF. grevous, grevos, LL. gravosus. See
   {Grief}.]
   1. Causing grief or sorrow; painful; afflictive; hard to
      bear; offensive; harmful.

            The famine was grievous in the land.  --Gen. xii.
                                                  10.

            The thing was very grievous in Abraham's sight.
                                                  --Gen. xxi.
                                                  11.

   2. Characterized by great atrocity; heinous; aggravated;
      flagitious; as, a grievous sin. --Gen. xviii. 20.

   3. Full of, or expressing, grief; showing great sorrow or
      affliction; as, a grievous cry. -- {Griev"ous*ly}, adv. --
      {Griev"ous*ness}, n.

Source : WordNet®

grievous
     adj 1: causing fear or anxiety by threatening great harm; "a
            dangerous operation"; "a grave situation"; "a grave
            illness"; "grievous bodily harm"; "a serious wound";
            "a serious turn of events"; "a severe case of
            pneumonia"; "a life-threatening disease" [syn: {dangerous},
             {grave}, {serious}, {severe}, {life-threatening}]
     2: causing or marked by grief or anguish; "a grievous loss"; "a
        grievous cry"; "her sigh was heartbreaking"; "the
        heartrending words of Rabin's granddaughter" [syn: {heartbreaking},
         {heartrending}]
     3: of great gravity or crucial import; requiring serious
        thought; "grave responsibilities"; "faced a grave decision
        in a time of crisis"; "a grievous fault"; "heavy matters
        of state"; "the weighty matters to be discussed at the
        peace conference" [syn: {grave}, {heavy}, {weighty}]
     4: shockingly brutal or cruel; "murder is an atrocious crime";
        "a grievous offense against morality"; "a grievous crime";
        "no excess was too monstrous for them to commit" [syn: {atrocious},
         {flagitious}, {heinous}, {monstrous}]