The noun has 2 meanings:
Meaning #1:
sitting on eggs so as to hatch them by the warmth of the body
Synonym: incubation
Meaning #2:
persistent morbid meditation on a problem
Synonym: pensiveness
The adjective brooding has 2 meanings:
Meaning #1:
persistently or morbidly thoughtful
Synonyms: broody, contemplative, meditative, musing, pensive, pondering, reflective, ruminative
Meaning #2:
good at incubating eggs especially a fowl kept for that purpose
Synonyms: brood, hatching
