Nouns

(n)brooding, incubationsitting on eggs so as to hatch them by the warmth of the body
(n)pensiveness, broodingpersistent morbid meditation on a problem

Adjectives

(s)brooding, broody, contemplative, meditative, musing, pensive, pondering, reflective, ruminativedeeply or seriously thoughtful“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”