If you know your Latin roots, you’ll know exactly what this one means. To obnubilate is “to obscure” or “cloud over”.
World Wide Words explains that obnubilate is a rare word today, but it had its uses:
Nineteenth-century reviewers used it to suggest that a writer had been less than transparently clear in his exposition, as here in a squib in The Princeton review in 1832 about a book by Samuel Taylor Coleridge: