Where does “Shemini Atzeret” come from?

Shemini Atzeret (English) comes from Hebrew שְׁמִינִי עֲצֶרֶת.

Ancestry of “Shemini Atzeret”, step by step

Step	Language	Word	Meaning
1	Hebrew	שְׁמִינִי עֲצֶרֶת	—

Shemini Atzeret — Etymology, Origin & Word History | Etymology Explorer