Ponzu

Ponzu ( Japanese pronunciation: [pondzɯ]) is a citrus-based sauce commonly used in Japanese cuisine. It is tart, with a thin, watery consistency. Ponzu shōyu or ponzu jōyu (ポン酢醤油) is ponzu with soy sauce (shōyu) added, and the mixed dark brown product is widely referred to as simply ponzu. The term originally came into the Japanese language as ponsu as a borrowing of the now obsolete Dutch word pons, meaning punch as in a beverage made from fruit juices. The sour nature of this sauce led to the final -su being written with the character su (酢), meaning "vinegar".

Source: Wikipedia