Game concept
Powerful Family Attribute
The game also links it as Family Attribute.
From the game's encyclopedia
A Powerful Family Attribute is a set of bonuses associated with a House inside a Bureaucratic Realm. The Attribute benefits the members of the House, as well as the Liege.
Attributes are only active as long as the House is considered a Powerful Family, and the Family Attribute of a Dominant Family does not benefit their Liege.
The House Head can freely replace the Attribute at any given time.
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.
Powerful Family Attribute is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A Powerful Family Attribute is a set of bonuses associated with a House inside a Bureaucratic Realm." It is part of House Attribute. The game also links it as Family Attribute. Patch 1.20.1.2, from game/common/game_concepts/07_ep3_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/07_ep3_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.