Hmm

[hmm] /hmm/

interjection
1.
(used typically to express thoughtful absorption, hesitation, doubt, or perplexity.)
/mm/
interjection
1.
a sound made when considering or puzzling over something
/spelling pron hmmm/
interjection
1.
used to indicate hesitation, doubt, assent, pleasure, etc

representative of a sound made during contemplation or showing mild disapproval, attested from 1868, but this is probably a variation of the hum attested in similar senses from 1590s.

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high mobility multipurpose wheeled vehicle
HMO
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Hmong
[hmawng] /hmɔŋ/ noun, plural Hmongs (especially collectively) Hmong. 1. .

Hmp
hybrid multiprocessing
Hmpao
1. hexametazimepropyleneamine oxime 2. hexamethylpropyleneamine oxime