Inert means not reacting with anything. An inert gas, chemically inert, inert material.
The noble gases are the standard example, and their unreactivity is why argon fills light bulbs and welding shields. An inert ingredient in a pesticide is one with no active effect, though that does not make it harmless. Of a person it means motionless and unresponsive. Note that the Latin means without skill or art.
1adjectiveinertNot reacting with anything.
“Gold is so inert that ancient coins still shine after centuries underground.”
2adjectivemotionlessMotionless and unresponsive.
“The injured bird lay inert on the path, and we thought it was dead.”
inert is a quality of unreactiveness.
Latin iners means inactive or unskilled — in plus ars, art. Art and artisan come from the same skill.
Proto-Indo-European
*h₂er-
Latin
iners — inactive, inert
French
inerte
English, today
inert
From French inerte, from Latin iners (“inactive, inert”).
Etymology from Wiktionary, CC BY-SA