Absent-minded

so lost in thought that one does not realize what one is doing, what is happening, etc.; preoccupied to the extent of being unaware of one’s immediate surroundings.
contemporary examples

the boy genius geithner turned into an absent-minded professor when he filled in his tax returns.
obama’s strange obsession tina brown february 8, 2009

a rush of water spills from above, but not from the bottle of an absent-minded commuter or tipsy traveler.
leaky ceilings, catcalls, and uncaged pythons: 4 hours on nyc’s worst subway kevin zawacki august 7, 2014

historical examples

“absent-minded—the citizen,” muttered barlasch, returning to the kitchen, where he resumed his seat on a chair by the open door.
barlasch of the guard h. s. merriman

“of course,” repeated the great man, with a sort of absent-minded loftiness.
the secret agent joseph conrad

my mother looked down, presently, at him, and checked the absent-minded p-sses of her hand over lucy’s hair.
when grandmamma was new marion harland

his face was downcast and he put the dishes on the table in an absent-minded way.
the widow o’callaghan’s boys gulielma zollinger

thinking of him i almost talk like him in his absent-minded moments.
sonnie-boy’s people james b. connolly

it shows how absent-minded i am, for i ought to have thought of the wine long ago.
one day’s courtship robert barr

to be sure—excuse me—i am absent-minded; i do take it—that is to say, yes, i accept these lovely roses.
the flower girl of the chteau d’eau, v.1 (novels of paul de k-ck volume xv) charles paul de k-ck

she seemed to be thinking of something else and her answers were brief and absent-minded.
fair harbor joseph crosby lincoln

adjective
preoccupied; forgetful; inattentive