adj. incomprehensible
adv. incomprehensibly
n. incomprehension; the quality of being incomprehensible; an incomprehensible thing or idea
v. to make or become incomprehensible

[Dragonrend] was said to force a dragon to experience the concept of Mortality. A truly vonmindoraan... incomprehensible idea to the immortal dov.
(Paarthurnax, 0003FA43)

From mindoraan ‘to understand’ with the prefix vo- ‘un-, opposite of’.

Unknown whether the n is accidental and the intended word is vomindoraan, or if it is intentional for an unknown reason. Vonmindoraan does not appear in any other source besides the dialogue cited above.