The story
- Proto-Indo-European*tres-
- Proto-Indo-European*troséyeti
- Proto-Italic*troseō
- Latinterreō
- Latinterror
- Old Frenchterreur
- Middle Frenchterreur
- Middle Englishterrour
- Englishterror
- Latinterreō
- Proto-Indo-European*dʰeh₁-
- Proto-Italic*θakos
- Latinterrificus
- Frenchterrifique
- Englishterrific
- English todayterrification
From terror + -ification or alternatively terrific + -ation.
Etymology from Wiktionary, CC BY-SA 4.0.