What does the cryptic crossword clue "Palace of Versailles excursion not finishing soon (7)" mean?

The definition is "P". The wordplay uses a charade (building blocks). TRI (synonym="TRI") + ANON (synonym="”soon”") = TRIANON The answer is TRIANON.

Palace of Versailles excursion not finishing soon (7)

Guardian Cryptic #29337 | 15 Across | 2024-03-22 flower