un
word
Definition
A prefix added to some words to mean “not,” “the opposite of,” or “to reverse an action.” For example, it appears in words like “unhappy,” “unsafe,” and “undo.”
Usage & Nuances
This is not usually a standalone word in modern English; it is mainly a prefix. It commonly attaches to adjectives ('unfair'), participles ('unfinished'), and some verbs ('unlock', 'undo'), but not every word can naturally take 'un-'. Learners should not add it freely to any adjective or verb.
Example Sentences
In unhappy, un means “not.”
basic
I knew un- usually meant “not,” but I didn’t realize it could also mean “reverse the action.”
natural
Once you understand un, words like unhappy and unfair become much easier to guess.
natural
We add un to some words to make the opposite meaning.
basic
The word undo uses un to show reversal.
basic
You can’t just put un in front of every adjective and expect it to sound natural.
natural