Leprechaun (3)
I believe the answer is:
elf
'leprechaun' is the definition.
(I have seen 'A leprechaun' mean 'elf' so perhaps 'leprechaun' could also mean 'elf')
This is the entire clue.
(Other definitions for elf that I've seen before include "He causes mischief" , "spirit" , "Imaginary small being with magic powers" , "Brownie" , "Dwarf" .)