incidental
adj.happening as a small part of something else, or by chance. It describes things that are not the main focus but still happen alongside it.
adj.occurring as a minor accompaniment to something else, or by chance. Often describes secondary consequences or costs that arise during a primary activity.
“The music in the film is incidental to the story.”
“While the main goal was networking, the incidental benefits of the conference included learning about new software tools.”
“The researcher noted that the temperature change was merely incidental and did not significantly affect the final outcome of the chemical reaction.”
Often used attributively before a noun or predicatively after a linking verb like 'be' or 'seem'.
“It seems to be the late 1990s, but that date feels almost incidental.”
“These three forms of online content aren't incidental features of online life.”
From incident + -al.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.