adj. (formal)
25B6; adjective
his death was a grievous blow : SERIOUS, severe, grave, bad, critical, dreadful, terrible, awful, crushing, calamitous; painful, agonizing, traumatic, wounding, damaging, injurious; sharp, acute.
a grievous sin : HEINOUS, grave, deplorable, shocking, appalling, atrocious, gross, dreadful, egregious, iniquitous.
slight, trivial.