"absorbed in thought, meditative," 1823, past-participle adjective from preoccupy (v.) in the "absorb mentally" sense. Earlier it meant "occupied in advance."
Entries linking to preoccupied
preoccupy v.
1560s, "engage (the attention of) beforehand, engross in advance of or to the exclusion of other things," from pre- "before" + occupy. Sense of "occupy before others" is attested from 1620s. Related: Preoccupied; preoccupying.