FiO2

Initialism of fraction [of] inspired + O₂ (“oxygen”).
Etymology tree
Middle English fraccioun
English fraction
Proto-Indo-European *h₂ep
Proto-Indo-European *-o
Proto-Indo-European *h₂epó
Proto-Germanic *ab
Proto-West Germanic *ab
Old English æf
Old English of
Middle English of
English of
English inspired
Proto-Indo-European *h₂eḱ-der.?
Ancient Greek ὀξύς (oxús)
Proto-Indo-European *ǵenh₁-
Proto-Indo-European *-os
Proto-Indo-European *ǵénh₁os
Proto-Hellenic *génos
Ancient Greek γένος (génos)
French oxygènebor.
English oxygen
English FiO2