Mac Dictionary defines it as:
Thick liquid served with food, usually savory dishes, to add moistness and flavor : tomato sauce | the cubes can be added to soups and sauces.
• stewed fruit, esp. apples, eaten as dessert or used as a garnish.
2 ( the sauce) informal alcoholic drink : she’s been on the sauce for years.
3 informal chiefly Brit. impertinence.
verb [ trans. ]
1 (usu. be sauced) provide a sauce for (something); season with a sauce.
• figurative make more interesting and exciting.
2 informal be rude or impudent to (someone).
what’s sauce (or good) for the goose is sauce (or good) for the gander proverb what is appropriate in one case is also appropriate in the other case in question.
ORIGIN Middle English : from Old French, based on Latin salsus ‘salted,’ past participle of salere ‘to salt,’ from sal ‘salt.’ Compare with salad.
Because salads have sauces, CLEARLY.