Supernal is an adjective that means related to the sky or the heavens.
The Latin word supernus (soo PAIR noos) means above or superior. From that we get our word of the day which means anything that refers to the skies or heavens above us.
My great grandfather was deathly afraid of getting on a plane. This was fairly common among people who grew up in the days when supernal travel was new and believed to be dangerous.