Englishabsentminded
adjective
an absentminded boffin:
forgetful, distracted, preoccupied, inattentive, vague, absorbed, abstracted, unheeding, oblivious, distrait, in a brown study, woolgathering;
lost in thought, pensive, thoughtful, brooding;
informal scatterbrained, miles away, with a mind/memory like a sieve.
▷antonyms alert, observant.