In Moby-Dick, what does craven mean?

Nobody likes being called a coward, but the offense is slightly better than being labeled craven. Craven is an adjective meaning very cowardly. As a noun, it refers to one who is a thorough coward.

In Moby-Dick, Ishmael introduces some of the ship's crew, including Stubb, the easy-going second mate:

He was a native of Cape Cod; and hence, according to local usage, was called a Cape-Cod-man. A happy-go-lucky; neither craven nor valiant; taking perils as they came with an indifferent air; and while engaged in the most imminent crisis of the chase, toiling away, calm and collected . . .