Mischievous thing eatin’ by the sound of it? (6)
I believe the answer is:
goblin
'mischievous thing' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'eatin' by the sound of it?' is the wordplay.
'eatin'' becomes 'gobblin'' ('gobbling' said like 'eating' was; gobbling is a kind of eating).
'by the sound of it?' shows a homophone (sound like).
'gobblin' is a homophone of 'GOBLIN'.
Can you help me to learn more?
(Other definitions for goblin that I've seen before include "Malevolent imp" , "Dwarf-like creature" , "Little monster" , "Evil imp" , "Mischievous sprite" .)