un- — not, opposite of, reversal of an action (affix)

unusual A2

/ʌnˈjuːʒ(u)əl/ Not usual or common; different from what you normally see Meaning Off Sound Off

unknown A2

/ʌnˈnoʊn/ Not known; not discovered or identified. Meaning Off Sound Off

unhappy A2

/ʌnˈhæpi/ Sad; not feeling happy. Meaning Off Sound Off

unable B1

/ʌnˈeɪbl̩/ Not able to do something; lacking the power, skill, or means. Meaning Off Sound Off

unfair A2

/ʌnˈfɛɚ/ Not fair; not treating people equally or in a just way. Meaning Off Sound Off

untie B2

/ʌnˈtaɪ/ To undo something that is tied, such as a knot or laces Meaning Off Sound Off

unlock B2

/ʌnˈlɑk/ To open something that is locked, usually with a key or code. Meaning Off Sound Off

undo B1

/ʌnˈduː/ To cancel or reverse something that has been done. Meaning Off Sound Off