What does the cryptic crossword clue "Row all but head of Trent tributary (3)" mean?

The definition is "Row". The wordplay uses a deletion. OAR (deletion) = OAR; definition: "Row" The answer is OAR.

Row all but head of Trent tributary (3)

Times Cryptic #28663 | 12 Across | 2023-07-24 flower