adjective

(of something bad) very severe or serious.

his death was a grievous blow

serious,severe,grave,bad,critical,dreadful,terrible,awful,painful,agonizing,hurtful,afflicting,wounding,damaging,injurious,sharp,acute,peracute,disastrous,calamitous,crushing,distressing,traumatic,harrowing,sorrowful,mournful,sad,heinous,deplorable,shocking,appalling,atrocious,gross,dire,outrageous,egregious,iniquitous,nefarious,shameful,lamentable,flagrant,glaring,flagitious