ex·ter·nal·ism \ekˈ ̷ ̷ ̷ ̷ˌizəm, ik-\noun (-s) 1. a.: externality 1a b.: attention to externals; especially: excessive preoccupation with externals < the externalism of some religions > 2.: a doctrine dealing only with immediate experience and with objects of sense perception and discounting the validity of other knowledge : phenomenalism