What does the cryptic crossword clue "Act ends surprisingly in additional vocal part (7)" mean?

The definition is "part". The wordplay uses an anagram. anagram of ACT + ENDS = DESCANT; definition: "part" The answer is DESCANT.

Act ends surprisingly in additional vocal part (7)

Daily Mail Cryptic #17289 | 12 Across | 2024-02-08 flower