WordNet sense 1 ((frequently plural) an expense not budgeted or not specified):

incidental expense, minor expense

WordNet sense 2 (following as a consequence):

attendant, concomitant, accompanying

WordNet sense 3 (being connected either logically or causally or by shared characteristics ):

related, related to

WordNet sense 4 (depending on or incidental to what is original or primary):

secondary

WordNet sense 5 ((sometimes followed by `to') minor or casual or subordinate in significance or nature or occurring as a chance concomitant or consequence):

incident

WordNet sense 6 (not of prime or central importance):

nonessential

WordNet sense 7 (not basic or fundamental):

inessential, unessential