English
reactionless
From reaction + -less.
Formed from reaction + -less
Proto-Indo-European *h₂eǵ- ‘to drive’
…
Latin reagō ‘to act upon again; to react’
Latin reāctiō ‘reaction’
Old French reaction
Middle English reaccion
English reaction
Today it means
adj Devoid of reactions; not reacting.
Language periods are conventional ranges, not dates for this word.
Etymograph / reactionless