The story
- Proto-Indo-European*dwóh₁
- Proto-Indo-European*dwi-
- Proto-Italic*dwi-
- Latinbi-
- Proto-Indo-European*med-
- Proto-Indo-European*meh₁-?
- Proto-Indo-European*mḗh₁n̥s
- Proto-Italic*mēns
- Proto-Italic*mēnsis
- Latinmēnsis
- Latinbimēnstrisbf.
- Latinannuusinflu.
- Latinmēnstruus
- Latinmēnstruum
- Englishmenstruum
- Late Latinmenstruatioinflu.
- English todaymenstruation
From menstruum + -ation, modelled after Late Latin menstruatio. The word is a cognate with French menstruation, Spanish menstruación, which displaced Old English mōnaþblōd (literally “monthblood”).
Etymology from Wiktionary, CC BY-SA 4.0.