Finally, much ado. Cause? An implement (3)
I believe the answer is:
hoe
'an implement' is the definition.
(hoe is a kind of implement)
'finally much ado cause?' is the wordplay.
'finally' suggests the final letters.
The last letters of 'much ado cause' are 'HOE'.
(Other definitions for hoe that I've seen before include "Garden tool with a flat blade" , "Weeding tool" , "Weed" , "Purple gem" , "Weeder" .)