1640s, "hovering, persistently overhanging" (as a mother bird does her nest), from present participle of brood (v.); meaning "that dwells moodily" first attested 1818 (in "Frankenstein").
"action of incubating," c. 1400, verbal noun from brood (v.). Figuratively (of weather, etc.) from 1805; of mental fixations by 1873. Related: Broodingly.
Byron lives on not only in his poetry, but also in his creation of the `Byronic hero' - the persona of a brooding melancholy young man