Where does “mmHg” come from?

mmHg (Translingual) comes from Translingual Hg, from Latin hydrargyrus, from Ancient Greek ὑδράργυρος, from Ancient Greek ὕδωρ, from Proto-Hellenic *údōr — water.

Ancestry of “mmHg”, step by step

mmHg traces back through two separate lines of ancestry.

via Translingual Hg

Step	Language	Word	Meaning
1	Translingual	Hg	mercury
2	Latin	hydrargyrus	quicksilver (artificially prepared), mercury
3	Ancient Greek	ὑδράργυρος	quicksilver artificially prepared from cinnabar...
4	Ancient Greek	ὕδωρ	water; rainwater, rain; sweat
5	Proto-Hellenic	*údōr	water

via Translingual mm

Step	Language	Word	Meaning
1	Translingual	mm	millimeter
2	Translingual	M	Thousand; The thousandth
3	Ancient Greek	Μ	Mu; my
4	Ancient Greek	Μοῖρα	Fates
5	Proto-Hellenic	móřřā	—

Every word from Proto-Hellenic *údōr →Every word from Ancient Greek ὕδωρ →Every word from Ancient Greek ὑδράργυρος →