What does the cryptic crossword clue "In general, it must establish definitive check (6,4)" mean?

The definition is "definitive check". The wordplay uses a hidden word. hidden as above. We had this the other day. The answer is LITMUS TEST.

In general, it must establish definitive check (6,4)

Times Cryptic #28707 | 24 Across | 2023-09-13 flower