Marked by slowness, whether physical sluggishness or mental dullness. The author of Hebrews uses this adjective twice to rebuke his audience: they have become 'dull of hearing' (5:11)—slow to grasp spiritual truth—and he urges them not to be 'sluggish' but to imitate faithful predecessors (6:12). The term suggests not inability but laziness, a culpable slowness to respond to what should be clear. Classical usage pairs it with foolishness and forgetfulness, reinforcing the moral dimension.