Letter from relative seized by crook and wino (9)
I believe the answer is:
consonant
'letter' is the definition.
(I know that consonant is a type of letter)
'relative seized by crook and wino' is the wordplay.
'relative' becomes 'nan' (informal term for a grandmother).
'seized by' is an insertion indicator.
'crook' becomes 'con'.
'and' is a charade indicator (letters next to each other).
'wino' becomes 'sot' (both can mean someone who drinks too much).
'con'+'sot'='consot'
'nan' put into 'consot' is 'CONSONANT'.
'from' is the link.
(Other definitions for consonant that I've seen before include "B, C, D or F, perhaps?" , "Only one of Ouida's characters is" , "In agreement" , "One of several characters" , "sounding well together" .)