Where does “FiO2” come from?

FiO2 (English) comes from English fraction, from Middle English fraccioun, from Occitan fraccion, from Latin fractio, from Latin -tiō, from Latin dissertātiō, from Latin dissertus, from Latin disserere — small stone, pebble; gravel, rubble.

Ancestry of “FiO2”, step by step

FiO2 traces back through 3 separate lines of ancestry.

via English fraction

Step	Language	Word	Meaning
1	English	fraction	A part of a whole, especially a comparatively...
2	Middle English	fraccioun	a breaking
3	Occitan	fraccion	a part; fraction
4	Latin	fractio	the action of breaking; fraction
5	Latin	-tiō	tion, -ation, -ing
6	Latin	dissertātiō	(spoken) dissertation, discourse, disquisition
7	Latin	dissertus	arranged, disposed; explained
8	Latin	disserere	second-person singular future passive indicative...
9	Latin	dis-	asunder, apart, in two; reversal, removal;...
10	Latin	calceus	shoe
11	Latin	calx	limestone; chalk; the finish line
12	Ancient Greek	χάλιξ	small stone, pebble; gravel, rubble

via English of

Step	Language	Word	Meaning
1	English	of	API; Expressing distance or motion; "Expressing...
2	Middle English	of	of; off; until
3	Old English	of	of, from, off, out of
4	Old English	æf	of
5	Proto-Germanic	*ab	—
6	Proto-Indo-European	apó	—

via Translingual O₂

Step	Language	Word	Meaning
1	Translingual	O₂	—
2	Translingual	o	—
3	Etruscan	𐌏	—
4	Ancient Greek	ο	Lower-case omicron (ὂ μικρόν), the 15th letter of the ancient Greek alphabet. It represented the close-mid back rounded vowel. It is preceded by ξ and followed by π
5	Phoenician	𐤏	ayin; ʿayin
6	Egyptian	𓁹	—

Words derived from “FiO2”

SpO2/FiO2 ratio

Every word from Ancient Greek χάλιξ →Every word from Latin -tiō →Every word from Latin dis- →