As adjectives the difference between unachievable and unattainable
is that unachievable is that cannot be achieved (or only with great difficulty while unattainable is impossible to attain or reach; inaccessible, unobtainable or unapproachable; unable to accomplish; beyond limit.
As a noun unattainable is
anything that cannot be attained.
unattainable
English
Adjective
(
en adjective)
Impossible to attain or reach; inaccessible, unobtainable or unapproachable; unable to accomplish; beyond limit.
Noun
(
en noun)
Anything that cannot be attained.