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must 1 (mŭst)
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v.
v.aux.
1. To be obliged or required by morality, law, or custom: Citizens must register in order to vote.
2. To be compelled, as by a physical necessity or requirement: Plants must have oxygen in order to live.
3. Used to express a command or admonition: You must not go there alone. You simply must be careful.
4. To be determined to; have as a fixed resolve: If you must leave, do it quietly.
5.
a. Used to indicate inevitability or certainty: We all must die.
b. Used to indicate logical probability or presumptive certainty: If the lights were on, they must have been at home.
v.intr.
Archaic
To be required or obliged to go: "I must from hence" (Shakespeare).
n.
Something that is absolutely required or indispensable: Promptness on the job is a must. Comfortable boots are a must when going on a hike.

[Middle English moste, from Old English mōste, past tense of mōtan, to be allowed; see med- in the Appendix of Indo-European roots.]

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2017 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
 
must 2 (mŭst)
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n.
The quality or condition of being stale or musty.

[Probably back-formation from MUSTY.]

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2017 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
 
must 3 (mŭst)
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n.
The unfermented or fermenting juice expressed from fruit, especially grapes.

[Middle English, from Old English, from Latin mustum, from neuter of mustus, new, fresh.]

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2017 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
 
must 4 (mŭst)
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n.
Variant of musth.

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2017 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
 
must 5 (mŭst)
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n.
Musk.

[Scottish, from Old French, variant of musc; see MUSK.]

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2017 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
 

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