Synonyms for Achievable:

adj.

attainable (adjective)
available, feasible, workable, practicable, obtainable, attainable, possible.
doable (adjective)
attainable, feasible, obtainable.
operable (adjective)
doable.

n.

achievable (noun)
realizable, doable, accomplishable, possible.

Other synonyms:

adj.
available, feasible, possible, practicable, realizable.
n.
accomplishable, attainable, doable, feasible, obtainable, practicable, realizable, workable.