Antonyms of adj excusable

2 senses of excusable

Sense 1
excusable (vs. inexcusable) -- (capable of being overlooked)

inexcusable (vs. excusable) -- (without excuse or justification)
        => indefensible, insupportable, unjustifiable, unwarrantable, unwarranted -- (incapable of being justified or explained)

Sense 2
excusable, forgivable, venial -- (easily excused or forgiven; "a venial error")

INDIRECT (VIA pardonable) -> unpardonable -- (not admitting of pardon; "unpardonable behavior")

Similarity of adj excusable

2 senses of excusable

Sense 1
excusable (vs. inexcusable) -- (capable of being overlooked)
       => justifiable -- (capable of being justified)

Sense 2
excusable, forgivable, venial -- (easily excused or forgiven; "a venial error")
       => pardonable (vs. unpardonable) -- (admitting of being pardoned)