u¹ or U (yū)
n., pl., u's, or U's, also us or Us.

1. The 21st letter of the modern English alphabet.
2. Any of the speech sounds represented by the letter u.
3. The 21st in a series.
4. Something shaped like the letter U.
5. U A grade that indicates an unsatisfactory status.

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The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.

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