Sound correspondence old granny kept in fancy cases (9)
I believe the answer is:
assonance
'sound correspondence' is the definition.
'assonance' can be an answer for 'correspondence' (I have seen 'Partial correspondence' mean 'assonance' so perhaps 'correspondence' could also mean 'assonance'). I'm not sure about the 'sound' bit.
'old granny kept in fancy cases' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'granny' becomes 'nan'.
'kept in' indicates putting letters inside.
'fancy' is an anagram indicator.
'o'+'nan'='onan'
'cases' with letters rearranged gives 'assce'.
'onan' placed into 'assce' is 'ASSONANCE'.
Can you help me to learn more?
(Other definitions for assonance that I've seen before include "Correspondence in sound" , "Resemblance of sound between syllables of nearby words" , "In poetry, resemblance in the sounds of words" , "sound agreement" , "Partial correspondence" .)