"sea-eagle, osprey," c. 1600, from Latin ossifraga "vulture," fem. of ossifragus, literally "bone-breaker," from ossifragus (adj.) "bone-breaking," from os (genitive ossis) "bone" (from PIE root *ost- "bone") + stem of frangere "to break" (from PIE root *bhreg- "to break").
By this name Pliny meant "the Lammergeier" (that name is from German and means literally "lamb-vulture"), a very large Old World vulture that swallows and digests bones and was believed also to drop them from aloft to break them and get at the marrow. But in England and France, the word was transferred to the osprey, perhaps on the basis of a rough similarity of sound between the two words.