mm Hg vs millimeter of mercury

mm Hg and millimeter of mercury both are nouns.

Word	Noun	Adjective	Verb	Adverb
mm Hg	Yes	No	No	No
millimeter of mercury	Yes	No	No	No

As nouns, mm Hg and millimeter of mercury are synonyms defined as:

mm Hg and millimeter of mercury: a unit of pressure equal to 0.001316 atmosphere; named after Torricelli

Other synonyms of mm Hg include torr.

mm Hg (noun)	millimeter of mercury (noun)
a unit of pressure equal to 0.001316 atmosphere; named after Torricelli	a unit of pressure equal to 0.001316 atmosphere; named after Torricelli