Lewis & Short

insessor, ōris, m. [insideo], a besetter, occupant (very rare); of a ship, Jul. Val. Res Gest. Alex. 1, 1: viarum, a waylayer, Symm. Ep. 2, 48; cf.: insessores, latrones, Paul. ex Fest. p. 111 Müll.: quod circa vias insidientur sedentes.