Likely is sometimes described as an adjective that looks like an adverb but it actually is an adverb too.
As an adjective, it has the meaning of 'probably going to happen' or 'probably true', as in ‘The most likely cause of the fire was a discarded cigarette end’. With the same meaning, likely can also be followed by an infinitive, as in 'The study shows that some people are more likely to suffer back problems than others', and by that plus a subordinate clause, as in 'It seems likely that interest rates will rise again’.
The expression more than likely means ‘almost certain', as in ‘It’s more than likely that the rules will be changed again in the near future'. With the meaning of 'suitable', likely can also be used before nouns such as candidate, successor and replacement, as in ‘She’s a likely candidate for the job’. If, on the other hand, you describe something as ‘a likely story’, usually in response to something you have just been told, you indicate that you do not believe it.
As an adverb, likely means ‘probably’ and is often used with quite, as in ‘They’ll quite likely ask you to pay a small deposit’. The phrase (as) likely as not is used to mean probably and is usually placed in initial position, as in ‘Likely as not they’ll be late again’.
Finally, you can use the expression not likely to say that you are definitely unwilling to do something, as in ‘Can I borrow your car? Not likely! Not with the way you drive’.