late 14c. as an order of angels, from Late Latin cherub, from Greek kheroub, from Hebrew kerubh (plural kerubhim) "winged angel," which according to Klein is perhaps related to Akkadian karubu "to bless," karibu "one who blesses," an epithet of the bull-colossus. Old English had cerubin, from the Greek plural. But there are other theories:
The cherubim, a common feature of ancient Near Eastern mythology, are not to be confused with the round-cheeked darlings of Renaissance iconography. The root of the terms either means "hybrid" or, by an inversion of consonants, "mount," "steed," and they are winged beasts, probably of awesome aspect, on which the sky god of the old Canaanite myths and of the poetry of Psalms goes riding through the air. [Robert Alter, "The Five Books of Moses," 2004, commentary on Genesis iii.24]
The meaning "beautiful child" is from 1705. The plural in this sense is cherubs.
in reference to the winged, human-like celestial creatures that hovered above God's throne in Isaiah's dream, 1667, a word first used by Milton (probably on analogy of cherub/cherubim), a back-formed singular from Seraphim (attested from Old English). An earlier singular in English was seraphin (1570s).
This is from Late Latin seraphim, from Greek seraphim, from Hebrew seraphim (only in Isaiah 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." The Late Latin word also was taken by early Christians as the name of a class of angels.