1. unyielding; stern, fierce; merciless, heartless, cruel; horrible, frightful. grimgrim , a. [compar. grimmer (-mer); superl. grimmest .] [as. grim; akin to g. grimm, equiv. to g. & d. grimmig, dan. grim, grum, sw. grym, icel. grimmr, g. gram grief, as adj., hostile; cf. gr. , a crushing sound, to neigh.] of forbidding or fear-inspiring aspect; fierce; stern; surly; cruel; frightful; horrible. whose grim aspect sets every joint a-shaking. the ridges of grim war