I was going to bring up the same claim—of it being a "Letter, from Robert Hooke to Gottfried Wilhelm Leibniz". It's clearly not written with that intent.

While reading, I first took it to be a journal entry. The penmanship also supports this. But the second person "you" at the end is a confounding detail. A journal entry in the form of a letter to himself is possible, but doesn't seem plausible.

The word you've labelled "[deviate?]" in your copy is definitely not "deviate" in the manuscript. I'm certain that the first letter is "R", and the second to last letter probably a "d" followed by "e" (compare to "undenyable" and "persuade"). The letter following "R" could be "i", but really could be anything. It's unfortunate that it's not as straightforward as just crafting a regex and grepping at /usr/share/dict/words, because whatever Hooke meant, it's likely to be an archaic spelling. "Recede" spelled as "Ricede" works grammatically, but I don't think that's it, either.

FYI I agree with you on that word: letter by letter it looks to me like "Roeade", but I can't figure out what English word that would be, either.