Synonyms for Grievous:

adj.

adverse (adjective)
disastrous, adverse, opposing, antipathetic, unfriendly, unfavorable, detrimental, perilous, troublesome, unpropitious, burdensome, unlucky, woeful, calamitous, distressful, tragic, untoward, catastrophic, inauspicious, difficult, unfortunate, miserable, hard.
all (adjective)
grave, severe, serious, dangerous.
disappointing (adjective)
heartbreaking.
egregious (adjective)
heinous.
painful (adjective)
disagreeable, grueling, miserable, offensive, distressful, bitter, biting, uncomfortable, insufferable, anguishing, wrenching, excruciating, horrendous, acute, Cramping, severe, Besetting, arduous, stabbing, odious, irritating, oppressive, agonizing, annoying, woeful, smarting, crushing, hurtful, trying, Irksome, sore, bothersome, stinging, Torturing., troublesome, inflaming, piercing, tormenting, aching, withering, aggravating, cutting, chafing, harrowing, Gnawing, painful, throbbing, sharp, unpleasant, unbearable, burdensome, cruel.
severe, painful; serious (adjective)
flagrant, weighty, oppressive, grave, sharp, hurtful, disturbing, troublesome, unbearable, tragic, agonizing, offensive, deplorable, dismal, upsetting, sorrowful, calamitous, heinous, sad, outrageous, villainous, pathetic, disquieting, lamentable, dire, heavy, monstrous, mournful, atrocious.

n.

dire, rigorous, extreme, desperate. help. atrocious (noun)
outrageous, villainous, flagrant.
distressing (noun)
disturbing, upsetting, disquieting.
grievous (noun)
heinous, atrocious, monstrous, critical, weighty, heavy, heartrending, heartbreaking, of import, grave, flagitious, serious, sorrowful, evil, important, severe, wicked, dangerous.
mournful (noun)
pathetic, sad, dismal.

Other synonyms:

lamentable, regrettable. deplorable, rueful. mournful. doleful, sad. mournful
dolorous.
Other relevant words:
outrageous, flagitious, critical, villainous, heavy, desperate, weighty, sad, serious, sorrowful, regrettable, disquieting, heartrending, wicked, grave, disturbing, sharp, important, extreme, lamentable, upsetting, pathetic, doleful, dismal, monstrous, atrocious, rueful, dolorous, of import, flagrant, evil, heinous, heartbreaking, dangerous, deplorable, mournful, dire.

Usage examples for grievous

  1. On his refusal, they declared that they would with a clear conscience, and for fear of incurring the divine wrath if they further delayed, proceed by all legitimate means to remove so grievous a scandal. – Studies from Court and Cloister by J.M. Stone
  2. The combat was passing sharp and grievous for the pagans advanced once more in rank and by companies. – Arthurian Chronicles: Roman de Brut by Wace
  3. Our fall, however, grievous as it was, was rendered more tolerable by the circumstance of having been prepared to expect it. – The History of the Rise, Progress and Accomplishment of the Abolition of the African Slave-Trade, by the British Parliament (1839) by Thomas Clarkson