Sounds a ghastly storyteller (5)
I believe the answer is:
grimm
'sounds a' is the definition.
I can't tell whether this definition defines the answer.
'ghastly storyteller' is the wordplay.
'ghastly' becomes 'grim' (I've seen this before).
'storyteller' becomes 'm' (I am not sure about this - if you are sure you should believe this answer much more).
'grim'+'m'='GRIMM'
Can you help me to learn more?
(Other definitions for grimm that I've seen before include "Fairy tale telling brother" , "The Brothers ..... wrote fairytales" , "Brothers who wrote fairy tales" , "writer" , "Old yarn collector" .)