Sine qua non is a noun that refers to an essential element.

The literal translation of our word of the day is ‘without which not.’ This is a helpful way to understand how to use our word of the day. For example: at cooking school, we didn’t learn about the using the oven for the first three months. This didn’t make sense, because the oven is the sine qua non of the kitchen. You could say that without an oven, a kitchen is just a big pantry with food.