English
fly ash
From fly (“(obsolete) act of flying”, noun) + ash.
A compound of fly ‘(obsolete) act of flying’ + ash
Proto-Indo-European *plew- ‘to fly, flow, run’
…
Proto-Germanic *fleugǭ ‘flying insect, fly’
Proto-West Germanic *fleugā ‘fly’
Old English flēge ‘a fly’
Middle English fflye
English fly
Proto-Indo-European *h₂eHs- ‘to be dry’
Proto-Germanic *askǭ
Proto-West Germanic *askā ‘ash, ashes’
Old English acse
Middle English aisshe
English ash
Today it means
noun A residue generated in the combustion of powdered coal or other materials, comprising the fine particles that rise with the flue gases; when generated industrially it is usually captured and can be recycled for use in construction materials.
Language periods are conventional ranges, not dates for this word.
Etymograph / fly ash