Sound correspondence old granny kept in broken 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 am not sure about the 'sound' bit.
'old granny kept in broken cases' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'granny' becomes 'nan'.
'kept' indicates putting letters inside.
'in broken' indicates anagramming the letters (I've seen this in other clues).
'o'+'nan'='onan'
'cases' with letters rearranged gives 'assce'.
'onan' inserted into 'assce' is 'ASSONANCE'.
Can you help me to learn more?
(Other definitions for assonance that I've seen before include "Audible agreement" , "The repetition of similar-sounding words or syllables" , "Correspondence in sound" , "In poetry, resemblance in the sounds of words" , "as spring sprung demonstrates?" .)