Synonyms for Forgetful:

adj.

all (adjective)
unretentive, short.
indifferent (adjective)
unconcerned.
neglectful (adjective)
slipshod, neglectful, inattentive, unmindful, haphazard, derelict, careless, shoddy, slovenly, inconsiderate, hit-and-miss, slapdash, bumbling, senile, perfunctory, thoughtless, sloppy, remiss, unheedful, Disregardful, inadvertent, clumsy, negligent, reckless.
tending to not remember (adjective)
preoccupied, dreamy, remiss, amnesic, inattentive, Absent-minded, sloppy, negligent, careless, neglectful, distracted, oblivious, heedless, unmindful.

n.

get/become lost (in something), oblivion, something goes in one ear and out the other, block, slip through the net/cracks, senior moment, mental block. heedless. remember. unthinking, unconcerned, unheeding, careful, unobservant. absentminded (noun)
preoccupied, Absent-minded, dreamy, distracted.
forgetful (noun)
short, amnesic, unretentive, amnesiac, oblivious, unmindful, mindless, inattentive.

Other synonyms:

unobservant, block, senior moment, unheeding, oblivion, mental block. heedless. unthinking. abstracted
Absent-minded.
Other relevant words:
unheeding, Absent-minded, short, dreamy, oblivious, unobservant, unretentive, unconcerned, amnesic, heedless, amnesiac, unthinking, mindless, block, distracted, preoccupied.

Usage examples for forgetful

  1. Sara said she really did not know what would happen to me some day if I was so careless and forgetful – Lucy Maud Montgomery Short Stories, 1905 to 1906 by Lucy Maud Montgomery
  2. Father, said the Duke, I am not forgetful of that duty. – Flemish Legends by Charles de Coster
  3. He grows broader and becomes forgetful of the trivial cares and prejudices of every- day life as he watches their development. – Garden Ornaments by Mary H. Northend