one-way • adj. moving or allowing movement in one direction only: a one-way valve. ∎ (of a road or system of roads) along which traffic may pass in one direction only. ∎ (of a ticket) allowing a person to travel to a place but not back again. ∎ (of glass or a mirror) seen as a mirror from one side but transparent from the other. ∎ denoting a relationship in which all the action or contribution of a particular kind comes from only one member: interaction between the organism and the environment is not a one-way process.