If either played another club, declarer would ruff on the board and sluff his diamond queen.
Used in the Beginning of Sentence
Declarer threw his queen of spades on the high diamond. He then won the last three tricks with his ace, queen and nine of hearts behind East's jack third.
Meaning of declarers for the defined word.
Grammatically, this word "declarers" is a noun, more specifically, a noun form.