lost in thought; showing preoccupation; "an absent stare"; "an absentminded professor"; "the scatty glancing quality of a hyperactive but unfocused intelligence"
deeply absorbed in thought; "as distant and bemused as a professor listening to the prattling of his freshman class"; "lost in thought"; "a preoccupied frown"
any of the more than 100 known substances (of which 92 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matter