likely -
has a good chance of being the case or of coming about; "these services are likely to be available to us all before long"; "she is likely to forget"; "a likely place for a restaurant"; "the broken limb is likely to fall"; "rain is likely"; "a likely topic for investigation"; "likely candidates for the job"
unlikely has little chance of being the case or coming about; "an unlikely story"; "an unlikely candidate for reelection"; "a butcher is unlikely to preach vegetarianism"
possible capable of happening or existing; "a breakthrough may be possible next year"; "anything is possible"; "warned of possible consequences"
apt,
liable (usually followed by `to') naturally disposed toward; "he is apt to ignore matters he considers unimportant"; "I am not minded to answer any questions"
probable apparently destined; "the probable consequences of going ahead with the scheme"
likely -
expected to become or be; in prospect; "potential clients"
prospective of or concerned with or related to the future; "prospective earnings"; "a prospective mother"; "a prospective bride"; "the statute is solely prospective in operation"
likely -
within the realm of credibility; "not a very likely excuse"