Princeton's WordNet

1. incidental expense, incidental, minor expense(noun)

   (frequently plural) an expense not budgeted or not specified

   "he requested reimbursement of $7 for incidental expenses"

2. incidental(adj)

   an item that is incidental

3. incidental, incident(adj)

   (sometimes followed by `to') minor or casual or subordinate in significance or nature or occurring as a chance concomitant or consequence

   "incidental expenses"; "the road will bring other incidental advantages"; "extra duties incidental to the job"; "labor problems incidental to a rapid expansion"; "confusion incidental to a quick change"

4. incidental, nonessential(adj)

   not of prime or central importance

   "nonessential to the integral meanings of poetry"- Pubs.MLA

5. attendant, consequent, accompanying, concomitant, incidental, ensuant, resultant, sequent(adj)

   following or accompanying as a consequence

   "an excessive growth of bureaucracy, with attendant problems"; "snags incidental to the changeover in management"; "attendant circumstances"; "the period of tension and consequent need for military preparedness"; "the ensuant response to his appeal"; "the resultant savings were considerable"

Kernerman English Learner's Dictionary

1. incidental(adjective)ˌɪn sɪˈdɛn tl

   less important than sth else; = secondary

   incidental costs; Her nationality is incidental to me.

Wiktionary

1. incidental(Noun)

   Incidental expense.

   She's costing us a lot in incidentals.

2. incidental(Adjective)

   Loosely associated; existing as a byproduct, tangent, or accident.

   That character, though colorful, is incidental to the overall plot.

3. incidental(Adjective)

   Entering or approaching, prior to reflection (more frequently incident).

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