THESAURUS
side issue
accession, accessory, accompaniment, addenda, addendum, additament, addition, additive, additory, additum, adjunct, adjuvant, annex, annexation, appanage, appendage, appendant, appurtenance, appurtenant, attachment, augment, augmentation, by-product, coda, complement, concomitant, continuation, corollary, extension, extrapolation, fixture, increase, increment, offshoot, outgrowth, pendant, reinforcement, side effect, supplement, tailpiece, undergirding
ROGET THESAURUS
side issue
Adjunct
N
adjunct, addition, additament, additum, affix, appelidage, annexe, annex, augment, augmentation, increment, reinforcement, supernumerary, accessory, item, garnish, sauce, accompaniment, adjective, addendum, complement, supplement, continuation, rider, offshoot, episode,
side issue, corollary, piece, flap, lappet, skirt, embroidery, trappings, cortege, tail, suffix, wing, additional, alate, alated, winged, in addition.