Definition of sub plumbo in US English:

sub plumbo

adverb

rare
  • With reference to a papal bull, apostolic letter, or other document: with the Pope's lead seal.

Origin

Early 16th century. From post-classical Latin sub plumbo from classical Latin sub + plumbō, ablative of plumbum.

Pronunciation

sub plumbo

/ˌsʌb ˈplʌmbəʊ/