Where does “ἀρνοῦμαι” come from?

ἀρνοῦμαι (Ancient Greek) comes from Ancient Greek ἀρνέομαι, from Proto-Indo-European h₂res-.

Ancestry of “ἀρνοῦμαι”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	ἀρνέομαι	to deny, disown; to refuse; to say "no", decline,...
2	Proto-Indo-European	h₂res-	—

ἀρνοῦμαι — Etymology, Origin & Word History | Etymology Explorer