Ponzu

 is a citrus-based sauce commonly used in Japanese cuisine. It is tart, with a thin, watery consistency and nearly colorless. 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 spelled with the character meaning "vinegar".
Ponzu is made by simmering mirin, rice vinegar, "katsuobushi" flakes (from tuna), and seaweed (kombu) over medium heat. The liquid is then cooled, strained to remove the "katsuobushi" flakes, and finally the juice of one or more of the following citrus fruits is added: "yuzu", "sudachi", "daidai", "kabosu", or lemon.
Commercial ponzu is generally sold in glass bottles, which may have some sediment. "Ponzu shoyu" is traditionally used as a dressing for "tataki" (lightly grilled, then chopped meat or fish), and also as a dip for "nabemono" (one-pot dishes) such as shabu-shabu. It is used as a dip for sashimi. In the Kansai region, it is offered as a topping for "takoyaki".