(1):

(a.) Not such as to inspire liking; unattractive; disagreeable.

(2):

(a.) Not likely; improbable; not to be reasonably expected; as, an unlikely event; the thing you mention is very unlikely.

(3):

(a.) Not holding out a prospect of success; likely to fail; unpromising; as, unlikely means.

(4):

(adv.) In an unlikely manner.