Unconcealed — in the past tense (5)
I believe the answer is:
'unconcealed' is the definition.
(associated in meaning)
'past tense' is the wordplay.
'past' becomes 'over' (both can mean finished).
'tense' becomes 't' (abbreviation used in many dictionaries).
'in the' is the link.
(Other definitions for overt that I've seen before include "Plain to see - manifest" , "Trove (anag.)" , "Openly displayed" , "Open and observable" , "Done or shown openly" .)