Game concept
Strong Hook
The game also links it as Strong Hooks.
From the game's encyclopedia
A Strong Hook is a very powerful Hook that you might have on a character who you have Blackmailed.
Strong Hooks are much more powerful than Weak Hooks, and can force someone to do terrible deeds for you — such as to become your Agent in a Murder (in addition to everything a Weak Hook can do!)
A Strong Hook also prevents the target from taking any hostile actions towards the holder.
Strong Hooks are not spent when used, but instead go on a cooldown before they can be used again. The passive effect is not lost when the Hook is used.
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.
Strong Hook is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A Strong Hook is a very powerful Hook that you might have on a character who you have Blackmailed." It is part of Hook. The game also links it as Strong Hooks. 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.