happening or likely to happen in an unplanned or subordinate conjunction with something else.

incurred casually and in addition to the regular or main amount

incidental expenses.

likely to happen or naturally appertaining (usually fol. by to ).

something incidental, as a circumstance.

incidentals, minor expenses.

adjective

basic , essential , fundamental , important , vital

adjective

accidental , accompanying , adventitious , ancillary , attendant , by-the-way , casual , chance , circumstantial , coincidental , concomitant , concurrent , contingent , contributing , contributory , fluke * , fortuitous , irregular , nonessential , occasional , odd , random , secondary , subordinate , subsidiary , adscititious , supervenient , accessory , added , adjunct , apropos , auxiliary , collateral , digressive , en passant , episodic , extraneous , helping , incidentally , interlocutory , intervenient , minor , oontingent , parenthetical , related , supplementary , tangential