incidental (adj.)

"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.

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Definitions of incidental from WordNet
incidental (adj.)
not of prime or central importance; "nonessential to the integral meanings of poetry"- Pubs.MLA;
Synonyms: nonessential / accidental
incidental (adj.)
(sometimes followed by `to') minor or casual or subordinate in significance or nature or occurring as a chance concomitant or consequence;
labor problems incidental to a rapid expansion
extra duties incidental to the job
incidental expenses
the road will bring other incidental advantages
confusion incidental to a quick change
Synonyms: incident
incidental (adj.)
occurring with or following as a consequence;
snags incidental to the changeover in management
incidental (n.)
(frequently plural) an expense not budgeted or not specified;
he requested reimbursement of $7 for incidental expenses
Synonyms: incidental expense / minor expense
incidental (n.)
an item that is incidental;