Word Origin & History
1667, first used by Milton (probably on analogy of cherub/cherubim), singular back-formation from O.E. seraphim (pl.), from L.L. seraphim, from Gk. seraphim, from Heb. seraphim (only in Isa. vi), pl. of *saraph (which does not occur in the Bible), probably lit. "the burning one," from saraph "it burned."
Seraphs were traditionally regarded as burning or flaming angels, though the word seems to have some etymological sense of "flying," perhaps from confusion with the root of Ar. sharafa "be lofty." Some scholars identify it with a word found in other passages interpreted as "fiery flying serpent."