Incidental (adjective)

1. Happening or arising as a chance or minor consequence or result.
2. Of secondary importance or not essential to the main purpose or matter.

Origin:

From late latin incidentalis, from latin incidens, present participle of incidere ("to fall upon, happen, occur"), from in- + cadere ("to fal.l")

Examples:

1. The company incurred some incidental expenses while travelling to the conference.
2. The book covers not only the main topic but also several incidental subjects.
3. The appearance of the singer was incidental to the main event, which was the comedy show.
4. The damages to the car were incidental and not covered under the insurance policy.
5. He received a prize as an incidental benefit of participating in the contest.