The story
- Proto-Indo-European*h₂erǵ-
- Proto-Indo-European*h₂érǵus
- Proto-Italic*argusder.?
- Latinarguō
- Latinargūmentum
- Latinargūmentor
- Medieval Latinargūmentātīvus
- Middle Englishargumentatif
- Englishargumentative
- English todayargumentatively
From argumentative + -ly.
Etymology from Wiktionary, CC BY-SA 4.0.