Thenceforth means from that time forward. When something happens thenceforth, it continues from a specific moment onward into the future.

You might read in a history book that after winning independence in 1776, America was thenceforth its own nation, no longer ruled by Britain. Or imagine a story where a character makes a promise and thenceforth keeps it faithfully for the rest of her life.

The word appears most often in formal writing, historical accounts, and literature. A biography might say that after moving to Paris in 1920, the artist lived and worked there thenceforth. It marks a turning point: before this moment, things were one way; from this point forward, they’re different.

Thenceforth is similar to thereafter or from then on, but it has a more formal, old-fashioned ring. You probably wouldn’t use it when telling your friend about your weekend, but you might encounter it in classic novels or historical documents where the language is more elevated and serious.