Partially means to some extent, but not entirely. Partially sighted, partially cooked, partially successful.
Partially sighted is the formal term for serious sight loss that is not total, and it is a legal category. The useful distinction from partly is that partly divides a whole into parts, and partially describes something incomplete.
1adverbpartiallyTo some extent, but not entirely.
“The road is partially closed while workers repair the bridge.”
partially is a degree.
Latin
partiālis — of or pertaining to a part
Old French
parcial — biased or particular
Middle English
partiall
English
partial
English, today
partially
From partial + -ly. partial comes from Middle English partiall, parcial, from Old French parcial (“biased or particular”), from Latin partiālis (“of or pertaining to a part”), from Latin pars (“part”).
Etymology from Wiktionary, CC BY-SA