What is the X in X-mas?
1640s, from French inerte (16c.) or directly from Latin inertem (nominative iners) "unskilled, inactive, helpless, sluggish, worthless," from in- "without" + ars (genitive artis) "skill" (see art (n.)). Originally of matter; specifically of gases from 1885. Of persons or creatures, from 1774.
inert in·ert (ĭn-ûrt')
Sluggish in action or motion; lethargic.
Not readily reactive with other chemical elements; forming few or no chemical compounds.
Having no pharmacologic or therapeutic action.