What pho side dish is described as vinegared white onions?

The pho side dish described as vinegared white onions is hành dấm. It is a sharp, crunchy accompaniment made by soaking white onion in vinegar.

The onion garnish provides acidity against pho’s savory, aromatic broth. Thinly sliced white onion is commonly pickled or dressed with vinegar, producing a bright contrast to beef, marrow-rich stock, and noodles. In Hanoi-style pho traditions, hành dấm may be ordered separately rather than automatically placed in every bowl.

Hành dấm is easy to confuse with the fresh onion and scallion toppings already found in many bowls. Those add sweetness and fragrance, while the vinegar-treated onion supplies a distinctly sour note. It is also different from nước béo, the extra-fatty broth, and from tương ớt, chili sauce. The pairing illustrates a broader Vietnamese cooking principle: rich foods are often balanced with herbs, pickles, and acidic condiments.