Mischief that makes very big waves (3)
I believe the answer is:
elf
'mischief' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for elf that I've seen before include "Dwarf" , "Fairy-like creature" , "Goblin" , "German team?" , "spirit" .)