adjective

very serious or gloomy.

his grim expression

stern,forbidding,uninviting,unapproachable,aloof,distant,formidable,strict,dour,harsh,steely,flinty,stony,fierce,ferocious,threatening,menacing,mean-looking,cross,churlish,crabbed,surly,sour,ill-tempered,unsmiling,cruel,ruthless,merciless,boot-faced