The act or an instance of resisting or the capacity to resist. A force that tends to oppose or retard motion. An underground organization engaged in a struggle for national liberation in a country under military or totalitarian occupation. Psychology A process in which the ego opposes the conscious recall of anxiety-producing experiences. Biology The capacity of an organism to defend itself against a disease. Biology The capacity of an organism or a tissue to withstand the effects of a harmful environmental agent. Electricity The opposition of a body or substance to current passing through it, resulting in a change of electrical energy into heat or another form of energy.