Where does “итак” come from?

итак (Russian) comes from Russian и, from Greek η, from Ancient Greek ἡ, from Proto-Hellenic *hā́, from Proto-Indo-European séh₂, from Proto-Indo-European só — this; that.

итак (Russian): so, now, right, okay (used at or near the beginning of a sentence, which is a logical conclusion from the previous one; corresponds in meaning to the terms 'thus', 'as a result', 'consequently')

Definitions

so, now, right, okay (used at or near the beginning of a sentence, which is a logical conclusion from the previous one; corresponds in meaning to the terms 'thus', 'as a result', 'consequently')

Ancestry of “итак”, step by step

итак traces back through two separate lines of ancestry.

via Russian и

Step	Language	Word	Meaning
1	Russian	и	and
2	Greek	η	nominative feminine singular of ο
3	Ancient Greek	ἡ	feminine nominative singular of ὁ
4	Proto-Hellenic	*hā́	that (demonstrative)
5	Proto-Indo-European	séh₂	—
6	Proto-Indo-European	só	this; that

via Russian так

Step	Language	Word	Meaning
1	Russian	так	so, thus; like that; so much
2	Old East Slavic	тако	so, like that
3	Proto-Slavic	tako	thus, so, in such a way
4	Proto-Slavic	takъ	such, such a (kind of), of that kind

Every word from Proto-Indo-European só →Every word from Proto-Indo-European séh₂ →Every word from Proto-Hellenic *hā́ →