How do you speak the word delicious in french?

You would use délicieux for a masculine noun, like "This cake is delicious" ("Ce gâteau est délicieux").

You would use délicieuse for a feminine noun, like "This soup is delicious" ("Cette soupe est délicieuse").

You can also use the singular délicieux for both masculine and feminine nouns when talking about the food itself, without specifying a particular noun, like "This is delicious!" ("C'est délicieux!").