IPA: //ʌnˈfʌnɪst//
KK: /ʌnˈfʌnɪst/
The least funny; something that does not make people laugh at all.
That joke was the unfunniest I've ever heard.
Unfunniest → It is formed from the prefix "un-" (meaning not) and the root "funny" (from Old English *funnig*, meaning causing laughter) combined with the superlative suffix "-est" (meaning most). The word "unfunniest" means the most not funny or the least funny.
Think of 'not' ('un-') and something that causes laughter ('funny') — when you say 'unfunniest', you're describing something that is the least capable of making you laugh.
No commonly confused words.