Where does “ἀμφιθέᾱτρον” come from?

ἀμφιθέᾱτρον (Ancient Greek) comes from Ancient Greek ἀμφί, from Ancient Greek ὀξύς, from Proto-Indo-European h₂eḱ- — sharp.

Ancestry of “ἀμφιθέᾱτρον”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	ἀμφί
2	Ancient Greek	ὀξύς	sharp, pointed; sharp, keen; quick, hasty, swift
3	Proto-Indo-European	h₂eḱ-	sharp

ἀμφιθέᾱτρον — Etymology, Origin & Word History | Etymology Explorer