What does the cryptic crossword clue "Dull whisky (litre declined) (3)" mean?

The definition is "Dull". The wordplay uses a deletion. MAT (deletion) = MAT; definition: "Dull" The answer is MAT.

Dull whisky (litre declined) (3)

Times Cryptic #28447 | 2 Down | 2022-11-14 flower