"casual, occurring casually in connection with something else; of minor importance," 1640s, from Medieval Latin incidentalis, from incidens (see incident (n.)). The earlier adjective in this sense was incident (1520s). Incidentals (n.) "'occasional' expenses, etc.," is attested by 1707. Incidental music "background music," originally in operas, is from 1812.
updated on March 18, 2016