What is the origin of memoriter?

Memoriter is a direct borrowing from Latin, in which the word has the same meaning, formed from the adjective memor “remembering” and the adverbial suffix –ter. Memor is the source of English commemorate, memorize, memorial, and many other words related to recollection. While English uses –ly to create adverbs from other parts of speech, Latin uses suffixes such as –ter, as we can see in other Latin-derived adverbs such as instanter “immediately.” Another such suffix is –ātim, as in verbatim “word for word” and literatim “letter for letter.”