apropos
adj
1 applicable, apposite, appropriate, apt, befitting, belonging, correct, fit, fitting, germane, meet (archaic) opportune, pertinent, proper, related, relevant, right, seemly, suitable, to the point, to the purpose
adv
2 appropriately, aptly, opportunely, pertinently, relevantly, suitably, timely, to the point, to the purpose
3 by the bye, by the way, incidentally, in passing, parenthetically, while on the subject
apropos of
prep in respect of, on the subject of, re, regarding, respecting, with reference to, with regard to, with respect to