What does the cryptic crossword clue "Grit is swirling in Asian river (6)" mean?

The definition is "river". The wordplay uses an anagram. anagram of GRIT + IS = TIGRIS; definition: "river" The answer is TIGRIS.

Grit is swirling in Asian river (6)

Daily Mail Cryptic #17167 | 16 Across | 2023-08-21 flower