Loyalty

Loyalty is an enchantment applied to tridents that causes a thrown trident to fly back to the player who threw it after it lands.

Loyalty can be obtained from enchanting tables, drops from mobs that have spawned in a raid,‌[Bedrock Edition only] books obtained by fishing, monster room chests, librarian villagers, and non-village structure loot.

The speed of returning depends on the level. When the trident hits an entity or 5 ticks (0.25 seconds) after hitting a block, the trident will begin returning. Once activated, it travels at a maximum speed of ~0.83 blocks per tick (~16.67 blocks per second) at level I, ~1.67 blocks per tick (~33.33 blocks per second) at level II, and 2.5 blocks per tick (50 blocks per second) at level III. Each level afterwards increases the trident's speed by ~0.83 blocks per tick (~16.67 blocks per second).