What does the cryptic crossword clue "First signs of tool under big container (3)" mean?

The definition is "container". The wordplay uses acrostic. first letters of "tool under big" = TUB; definition: "container" The answer is TUB.

First signs of tool under big container (3)

Daily Mail Cryptic #17120 | 22 Across | 2023-06-15 flower