ob·sess / əbˈses/ • v. [tr.] (usu. be obsessed) preoccupy or fill the mind of (someone) continually, intrusively, and to a troubling extent: he was obsessed with thoughts of suicide| [as adj.] (obsessed) he became completely obsessed about germs. ∎ [intr.] (of a person) be preoccupied in this way: her husband, who is obsessing about the wrong she has done him. DERIVATIVES: ob·ses·sive / -ˈsesiv/ adj. & n. ob·ses·sive·ly / -ˈsesivlē/ adv. ob·ses·sive·ness / -ˈsesivnis/ n.