From The Collaborative International Dictionary of English v.0.48:
overt \o"vert\ ([=o]*v[~e]rt" or [=o]"v[~e]rt), a. [OF. overt,
F. ouvert, p. p. of OF. ovrir, F. ouvrir, to open, of
uncertain origin; cf. It. aprire, OIt. also oprire, L.
aperire to open, operire to cover, deoperire to uncover.
Perh. from L. aperire influenced by F. couvrir to cover. Cf.
Aperient, Cover.]
[1913 Webster]
1. Open to view; public; apparent; manifest. Opposite of
hidden.
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Overt and apparent virtues bring forth praise.
--Bacon.
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2. (Law) Not covert; open; public; manifest; as, an overt act
of treason. --Macaulay.
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No person shall be convicted of treason unless on
the testimony of two witnesses to the same overt
act, or on confession in open court. --Constitution
of the U. S.
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Note: In criminal law, an overt act is an open act done in
pursuance and manifestation of a criminal design; the
mere design or intent not being punishable without such
act. In English law, market overt is an open market; a
pound overt is an open, uncovered pound.
[1913 Webster]