No, the translation of the Greek mysterion is the Latin mysterium, secret doctrine.
In the Greek, mysterion is something newly revealed, not revealed before.
I find no new information in your latest post compared to the previous one, hence I have nothing further to add. If you choose not to accept the definitions from a Latin to English lexicon, nor those from a Greek to Latin lexicon, you are entitled to your perspective. I take solace in the fact that those qualified to compile lexicons have offered clear definitions, and that Saint Jerome's work is a reference they consult.
An afterthought, just for reference:
μυστήριον τό, (< μύστης, μυέω)
mystery or
secret rite ; mostly in pl., τὰ μ.
the mysteries, first in
Heraclit. 14, cf.
Hdt. 2.51 (of
the mysteries of the Cabiri in Samothrace), etc. ; esp. those of Demeter at Eleusis,
A. Fr. 479,
S. Fr. 804,
E. Supp. 173,
Ar. Ra. 887, etc. ; μυστηρίοις τοῖς μείζοσιν, τοῖς ὀλείζοσιν μ., IG1². 6.93, 96 ; but usu., τὰ μεγάλα, τὰ μικρὰ μ., Sch.
Ar. Pl. 846, cf. IG1². 313.144, 2².1672.4,
Pl. Grg. 497c, etc. ; πρὸ τῶν μεγάλων μ. τὰ μικρὰ παραδοτέον
Iamb. Protr. 2 ; ἀπιέναι πρὸ τῶν μ., i.e. before you have reached the heart of the matter,
Pl. Men. 76e ; τὰ τῆς θεοῦ (sc. Μεγάλης Μητρὸς) μ. OGI 540.21 (Pessinus, i
AD) ; οἱ θεοὶ οἷς τὰ μ. ἐπιτελεῖται IG 5(1).1390.2 (Andania, i BC) ; τὰ μ. ποιεῖν
And. 1.11,
Lys. 14.42, cf.
Th. 6.28 (Pass.) ; μ. ἐρεῖν
And. l.c. ; later in sg., PMagLeid. W. 3.42 (ii/iii
AD).
mystic implements and
ornaments, σεμνὰ στεμμάτων μυστήρια
E. Supp. 470 ; esp.
properties, such as were carried to Eleusis at the celebration of the mysteries,
ὄνος ἄγω μυστήρια, prov. of an over-loaded beast,
Ar. Ra. 159. later,
object used in magical rites, talisman, δότε πνεῦμα τῷ ὑπ' ἐμοῦ κατεσκευασμένῳ μ. PMagLeid. V. 10.19 (iii/iv
AD).
metaph, ὕπνος, τὰ μικρὰ τοῦ θανάτου μ.
Mnesim. 11 ; τῆς Ῥωμαίων ἀρχῆς σεμνὸν μ., of the military
sacramentum,
Hdn. 8.7.4 ; generally,
mystery, secret,
Pl. Tht. 156a ; μυστήριόν σου μὴ κατείπῃς τῷ φίλῳ
Men. 695, cf.
LXX Si. 27.16, To. 12.7 ; προσήγγειλε τὰ μ. τοῖς πολεμίοις
ib. 2 Ma. 13.21 ; μυστήρια βίου
Sor. 1.3 ; τοὐμὸν τὸ μ. [the remedy] is my
secret,
Aret. CD 2.7 ; hence, of a medicine,
Gal. 13.96,
Alex.Trall. 5.4.
secret revealed by God, i.e.
religious or
mystical truth,
Corp.Herm. 1.16, etc. ; τὰ μ. τῆς βασιλείας τῶν οὐρανῶν
Ev. Matt. 13.11 ; πνεύματι λαλεῖν μυστήρια
1 Ep. Cor. 14.2 ; τὸ μ. τῆς ἀνομίας the
mystery of iniquity,
2 Ep. Thess. 2.7 ; τὸν Ἀντιπάτρου βίον οὐκ ἂν ἁμάρτοιτις εἰπὼν κακίας μ.
J. BJ 1.24.1 ; esp. of the Gospel or parts of it, τὸ μ. τοῦ εὐαγγελίου
Ep. Eph. 6.19, cf. 3.9,
Ep. Col. 1.26, al. ;
symbol, τὸ μ. τῶν ἑπτὰ ἀστέρων
Apoc. 1.20, cf. 17.7. σύνηθές τι μ. some vulgar
superstition,
Sor. 1.4. (
source)