Game concept

Rival

The game also links it as Rivals, Rival's, Rivals', Rivalries, Rivalry.

From the game's encyclopedia

A Rival is a Special Relation indicating life-long resentment, if not hatred.

Rivals who truly despise each other might become Nemeses.

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.

Rival is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A Rival is a Special Relation indicating life-long resentment, if not hatred." It is part of Special Relation. The game also links it as Rivals, Rival's, Rivals', Rivalries and 1 more. Patch 1.20.1.2, from game/common/game_concepts/00_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.

for a guide, post or blog

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.