Clue: Gruesome song with rare origins (4,1,4,6)
Answer: RING A RING O’ROSES
Explanation: Definition: Gruesome song with rare origins
An anagram ('gruesome') of 'song' plus 'rare origins'. The enumeration threw me for a while. What is now a children's song is said to have its origins in references to the Great Plague, so we have a true &lit.