The story
- Proto-Indo-European*h₁éǵʰ
- Proto-Indo-European*h₁éǵʰs
- Proto-Indo-European*h₁eǵʰsteros
- Proto-Italic*eksteros
- Latinexter
- Latinextrā
- Englishextra-
- English(inter)polate
- English todayextrapolate
From extra- + (inter)polate.
Etymology from Wiktionary, CC BY-SA 4.0.