grievous
adjective formal
(of something bad) very severe or serious:
｟かたく｠ 〖通例名詞の前で〗深刻［重大］な〈過ち･犯罪･けがなど〉; 悲嘆すべき
e.g. his death was a grievous blow
e.g. the American fleet suffered grievous losses.
DERIVATIVES
grievousness noun
ORIGIN
Middle English: from Old French greveus, from grever (see grieve1).
USAGE
Grievous ends with -ous and has two syllables: do not pronounce it with three syllables (GREE-vee-us), as if it ended with -ious.