Wiktionary
n. (context humorous English) A hypothetical burn on the skin caused by excess exposure to moonlight.
Wikipedia
"Moonburn" is a 1935 American popular song written by Hoagy Carmichael and Edward Heyman. It was the first song written by Hoagy Carmichael for films and it was introduced by Bing Crosby in the 1936 film Anything Goes. A definitive jazz recording of the song was made by Crosby for Decca Records on November 13, 1935 with Georgie Stoll's Instrumental Trio featuring Bobby Sherwood on guitar and Joe Sullivan on piano.
Usage examples of "moonburn".
We are passing through the reservation of the Otoe Indians, who long ago washed the war-paint from their faces, buried the tomahawk, and settled down into quiet, prosperous farmers.
Several had told us of the Ponca and of their kinfolk the Omahas, Otoes, and Osages.