What does the cryptic crossword clue "D'Artagnan at once embraces group that's all for one (4)" mean?

The definition is "one". The wordplay uses a hidden word. Hidden in "d'artagnaN AT Once embraces group that's all for one" The answer is NATO.

D'Artagnan at once embraces group that's all for one (4)

Independent Cryptic #11620 | 11 Across | 2024-01-08 flower