Antonyms of adj understandable

1 sense of understandable

Sense 1
apprehensible, intelligible, graspable, perceivable, understandable -- (capable of being apprehended or understood)

INDIRECT (VIA comprehensible) -> incomprehensible, uncomprehensible -- (difficult to understand; "the most incomprehensible thing about the universe is that it is comprehensible"- A. Einstein)

Similarity of adj understandable

1 sense of understandable

Sense 1
apprehensible, intelligible, graspable, perceivable, understandable -- (capable of being apprehended or understood)
       => comprehensible (vs. incomprehensible), comprehendible -- (capable of being comprehended or understood; "an idea comprehensible to the average mind")