perhaps, possibly, can be, might be, could be, maybe so, mayhap, as it may be, conceivable, credible, feasible, obtainable, wind and weather permitting, in the cards*, God willing.
Antonyms hardly*, scarcely, probably not.
"maybe." YourDictionary, n.d. Web. 20 August 2018. <http://thesaurus.yourdictionary.com/MAYBE>.
maybe. (n.d.). Retrieved August 20th, 2018, from http://thesaurus.yourdictionary.com/MAYBE
Possibly but not certainly: