Game concept
Chancellor
The game also links it as Chancellors.
From the game's encyclopedia
The Chancellor is the Councillor in charge of diplomatic efforts, both inside and outside the Realm.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Chancellor is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "The Chancellor is the Councillor in charge of diplomatic efforts, both inside and outside the Realm." It is part of Councillor. The game also links it as Chancellors. Patch 1.20.1.2, from game/common/game_concepts/00_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/00_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.