The story
- Proto-Indo-European*deh₂-
- Proto-Indo-European*deh₂y-
- Proto-Indo-European*déh₂itis
- Proto-Indo-European*dih₂tís
- Proto-Germanic*tīdiz
- Proto-West Germanic*tīdi
- Old Englishtīd
- Middle Englishtide
- Englishtide
- Proto-Indo-European*h₂el-
- Proto-Indo-European*h₂élisder.?
- English todaytidal
From tide + -al. Probably a hybrid formation within English. Alternatively it might be from an unattested British Medieval Latin *tīdālis, derived from rare tīda, from Old English tīd. The usual Latin word for “tidal” is aestuālis.
Etymology from Wiktionary, CC BY-SA 4.0.