Stories We Like: A Guide to the Comma
1667, first used by Milton (probably on analogy of cherub/cherubim), back-formed singular from Old English seraphim (plural), from Late Latin seraphim, from Greek seraphim, from Hebrew seraphim (only in Isa. vi), plural of *saraph (which does not occur in the Bible), probably literally "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 Arabic sharafa "be lofty." Some scholars identify it with a word found in other passages interpreted as "fiery flying serpent."