There are 2 definitions of hm in English:

hm1

Syllabification: hm

abbreviation

Hectometer(s).

Definition of hm in:

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Word of the day premonition
Pronunciation: ˌprɛməˈnɪʃ(ə)n
noun
a strong feeling that something will happen …

There are 2 definitions of hm in English:

HM2

Syllabification: HM

abbreviation

1Headmaster or headmistress.
1.1(In the UK) Her (or His) Majesty('s): HM Forces

Definition of hm in: