Cailín Óg a Stór is a traditional Irish melody, originally accepted for publication in March of 1582. It may be the source of Pistol's cryptic line in Henry V

Henry V (play)

Henry V is a history play by William Shakespeare, believed to be written in approximately 1599. Its full titles are The Cronicle History of Henry the Fifth and The Life of Henry the Fifth...

, "Calen O custure".
It is part of a broadside

Broadside (music)

A broadside is a single sheet of cheap paper printed on one side, often with a ballad, rhyme, news and sometimes with woodcut illustrations...

 collection from 1584. The poem "The Croppy Boy

The Croppy Boy

"The Croppy Boy" is an Irish ballad set in 1798 rising and is one of the saddest ballads of the rebellion, relating the despair of a doomed young "croppy" or rebel.-Broadside versions:...

" was set to this music, and it was later used for the tune of "Lord Franklin", which was the basis for the Bob Dylan

Bob Dylan

Bob Dylan is an American singer-songwriter, musician, poet, film director and painter. He has been a major and profoundly influential figure in popular music and culture for five decades. Much of his most celebrated work dates from the 1960s when he was an informal chronicler and a seemingly...

 song "Bob Dylan's Dream

Bob Dylan's Dream

"Bob Dylan's Dream" is a song written by Bob Dylan in 1963. It was recorded by Dylan on April 24, 1963, and was released by Columbia Records a month later on the album The Freewheelin' Bob Dylan....

".