HM

Multiple Entries:
  HM    hm    hectometre  

Concise Oxford English Dictionary © 2008 Oxford University Press:
HM

▶abbreviation

• 1 headmaster or headmistress.

• 2 Brit. heavy metal (music).

• 3 (in the UK) Her or His Majesty('s).

Concise Oxford English Dictionary © 2008 Oxford University Press:
hm

▶abbreviation hectometre(s).

Concise Oxford English Dictionary © 2008 Oxford University Press:
hectometre /ˈhɛktə(ʊ)ˌmiːtə/ (US hectometer) (abbrev.: hm)

▶noun a metric unit of length equal to 100 metres.