Synonyms for Possibly:

adv.

attainably (adverb)
attainably, availably, achieveably, obtainably, practicably, workably, feasibly.
by chance; in some way (adverb)
maybe, peradventure, likely, perhaps, conceivably, probably, perchance.
possibly (adverb)
maybe, perchance, luckily, potentially, conceivably, imaginably, perhaps.
probably (adverb)
aptly, likely, probably, plausibly, feasibly, presumably.

adv

attainably (adverb)
attainably, availably, achieveably, obtainably, practicably, workably, feasibly.
possibly (adverb)
perchance, maybe, perhaps, conceivably, potentially, imaginably, feasibly, luckily.
probably (adverb)
plausibly, practicably, likely, probably, aptly, imaginably, presumably.

n.

is that a fact?, of all things/people/places, heavens above, Well, I never, you would not believe, you don't say, actually, now I've seen everything/it all, funnily enough, who would have thought...?. in principle, possible, feasible, practicable, be able to do something, humanly possible, attainable, may, doable, viable. keep, do with, just, what's gotten into someone?, where has someone/something gotten to?, what has/will become of, anyway, kindly, how, what (has) happened to something. expected, good, certain, probable, bound, sure, guaranteed. no-go, impossible, unbelievable, hardly, be out of the question, with the best will in the world, something will not work/start/open etc., impossibility. possibly (noun)
perhaps, maybe, potentially, perchance, peradventure.

Other synonyms:

impossibility, expected. guaranteed, unbelievable, probable. impossible. certain. bound. sure. good. Other relevant words:
hardly, possible, attainable, may, bound, doable, viable, certain, guaranteed, unbelievable, practicable, how, keep, impossibility, expected, probable, impossible, kindly, feasible, actually, good, peradventure, no-go, anyway, sure, just.

Usage examples for possibly

  1. I should like to know, for your happiness is as much to me as mine could possibly be to you." – A Woman Named Smith by Marie Conway Oemler
  2. I want you children to be as kind as you possibly can to Mrs. Golden. – Bunny Brown and His Sister Sue Keeping Store by Laura Lee Hope
  3. The following sentence cannot possibly be understood. – The Grammar of English Grammars by Goold Brown