Mischievous Irish elf (10)
I believe the answer is:
'mischievous irish elf' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for leprechaun that I've seen before include "Mischievous imp" , "Elf in Irish folklore" , "He helps Irish housewife" , "Mischievous Irish elf" , "Mischievous Irish sprite" .)