Though not featured in prose, they show sound correspondence (6)
I believe the answer is:
rhymes
'though not featured in prose they' is the definition.
The definition suggests a plural noun which matches the answer.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for rhymes that I've seen before include "Nursery . . . . . . are traditional verses for children" , "Pieces of verse" , "Nursery . . . . . . are children's poems" , "Similarities of word sounds as in verse" , "Nursery . . . . . . are simple ditties for children" .)