Patent finished on sixth of inventions (5)
I believe the answer is:
overt
'patent' is the definition.
(both can mean obvious)
'finished on sixth of inventions' is the wordplay.
'finished' becomes 'over' (similar in meaning).
'on' means one lot of letters go next to another.
'sixth of inventions' becomes 't' (6th letter of 'inventions').
'over'+'t'='OVERT'
(Other definitions for overt that I've seen before include "Openly displayed" , "Plain and obvious" , "Trove (anag.)" , "Open,up front" , "Open and obvious" .)