in petto

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in pet·to

 (ĭn pĕt′ō)
adv. & adj. Roman Catholic Church
In secret or private. Used of appointments of cardinals by the pope undisclosed in consistory.

[Italian : in, in + petto, breast.]

in petto

(ɪn ˈpɛtəʊ)
(Roman Catholic Church) RC Church not disclosed: used of the names of cardinals designate
[Italian, literally: in the breast]

in pet•to

(inˈpɛt tɔ)

adv., adj. Italian.
(of cardinals whom the pope appoints but does not disclose in consistory) in secret or private; not disclosed.
[literally, in (the) breast]
References in classic literature ?
Still they may entitle him to have this VETO, in petto.
Jeune Afrique a revele, hier mercredi 20 septembre 2017, que le gendre de Ben Ali a eu une entrevue in petto avec Rached Ghannouchi, le president Ennahdha et son gendre Rafik Bouchlaka, dans une villa a proximite de Doha, au Qatar.
13, 2003) consistently refers to him as a "former chancellor of the diocese of Rochester," which he has not been, unless in petto.