Crossword Genius

Mischief that makes very big waves (3)

Ross

I believe the answer is:

elf

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'mischief' is the definition.
(thesaurus)

I cannot understand how the remainder of the clue works.

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(Other definitions for elf that I've seen before include "Dwarf" , "Fairy-like creature" , "Goblin" , "German team?" , "spirit" .)

I've seen this clue in The Times.
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