noun

• Initialism of His Majesty (the title of a king).
• Initialism of Her Majesty (the title of a queen).
• (India, government) Initialism of Home Minister. [(India, government) The head of the Ministry of Home Affairs of the Government of India.]
• (military, US) Abbreviation of hospital corpsman. [(military, US, nautical) A member of a hospital corps, typically an enlisted navy sailor, often working at military hospitals.]
• (music) Abbreviation of heavy metal. [(sciences, countable) Any metal that has a specific gravity greater than about 5, especially one, such as lead, that is poisonous and may be a hazard in the environment. (There are many different definitions of what counts as a heavy metal; see Heavy metals for a discussion.)]
• (computing theory) Initialism of Hindley-Milner.