Antonyms of adj doable

1 sense of doable

Sense 1
accomplishable, achievable, doable, manageable, realizable -- (capable of existing or taking place or proving true; possible to do)

INDIRECT (VIA possible) -> impossible -- (not capable of occurring or being accomplished or dealt with; "an impossible dream"; "an impossible situation")

Similarity of adj doable

1 sense of doable

Sense 1
accomplishable, achievable, doable, manageable, realizable -- (capable of existing or taking place or proving true; possible to do)
       => possible (vs. impossible) -- (capable of happening or existing; "a breakthrough may be possible next year"; "anything is possible"; "warned of possible consequences")