What does the cryptic crossword clue "Thin, crisp biscuit — a marvellous thing! (7)" mean?

The definition is "Thin, crisp biscuit / a marvellous thing!". The wordplay uses a double definition. Double definition The answer is CRACKER.

Thin, crisp biscuit — a marvellous thing! (7)

Times Cryptic #28717 | 19 Down | 2023-09-25 flower