Where does “plain flour” come from?

plain flour (English) comes from English plain, from Middle English pleyn, from Anglo-Norman pleyn, from Old French playn, from Old French plain, from Latin plēnus, from Proto-Italic plēnos, from Proto-Indo-European pl̥h₁nós — to fill.

plain flour (English): A wheat flour with a medium gluten content,...

Definitions

  1. A wheat flour with a medium gluten content,...

Ancestry of “plain flour”, step by step

plain flour traces back through two separate lines of ancestry.

via English plain

StepLanguageWordMeaning
1EnglishplainFlat, level; Simple; Obvious
2Middle Englishpleynclear; unambiguous
3Anglo-NormanpleynAlternative form of plein
4Old Frenchplayn
5Old Frenchplainfull; plain; flat
6Latinplēnusfull; filled; complete
7Proto-Italicplēnosfull
8Proto-Indo-Europeanpl̥h₁nósfull
9Proto-Indo-Europeanpleh₁-to fill

via English flour

StepLanguageWordMeaning
1EnglishflourPowder obtained by grinding or milling cereal...
Every word from Proto-Indo-European pleh₁-Every word from Proto-Indo-European pl̥h₁nósEvery word from Proto-Italic plēnos