Parsley unit (5)
I believe the answer is:
sprig
'parsley unit' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sprig that I've seen before include "Small spray of leaves or flowers" , "Small branch or shoot" , "Small stem taken from a bush or plant" , "A tack; a little shoot" , "Small stem with leaves or flowers" .)