Prefix un-
Unhappy
Not happy
Ex: "My mother was unhappy when she came home and the dishes weren't done."
Unlock
To open or remove a lock that is preventing something from being accessible.
Ex: "Please unlock the door so we can get in the car."
Unfair
Not fair
Ex: "I thought it was unfair that my brother got to ride in the front seat of the car and I had to ride in the back."
Unable
Not able to do something
Ex: "I was unable to finish my assignment on time because I had to work."
Unwrap
To remove the cover or packaging from something
Ex: "She eagerly tore the colorful wrapping paper to unwrap her Birthday present."
Unpaid
Not paid or compensated for doing something
Ex: "Billy's allowance had been unpaid for weeks because he hadn't finished his chores, so he decided to finally clean his room to earn it back."
Unknown
Not known
Ex: "The person who sent the anonymous letter remains unknown."
Uncommon
Ex: Finding a four-leaf clover may be uncommon, but if you do, that means good luck!
Unpack
To remove items from a bag or box
Ex: "I unpacked my suitcase right when I got back from vacation."
Unfinished
Not finished
Ex: "She left her painting unfinished."
Unacceptable
Not acceptable
Ex: "Skipping class is unacceptable."
Unclear
Not clear, vague
Ex: "The directions were unclear on the treasure map, so we couldn't tell where "X" marked the spot to find the hidden treasure chest."
Unpredictable
Not predictable
Ex: "The weather can be unpredictable sometimes."
Unforgettable
Memorable, leaving a lasting impression
Ex: "The day we visited the zoo and saw polar bears swimming was unforgettable!"
Uncomfortable
Not comfortable, not at ease
Ex: "Wearing that itchy, tight sweater for the school play made me uncomfortable and I couldn't wait to take it off!"