What is "pickled onion"

n. (context British English) An onion that has been pickling in vinegar. It is often served as a bar snack in British pubs, and as part of a salad or ploughman's lunch.

Pickled onions are a food item consisting of onions pickled in a solution of vinegar and salt, often with other preservatives and flavourings. In the United Kingdom they are often eaten alongside fish and chips or as part of a ploughman's lunch. There is a variety of small white pickled onions known as 'silverskin' onions, frequently used as an essential component of the Martini cocktail variant known as a Gibson.

Pickled onions are usually pickled in malt vinegar and the onions are about an inch in diameter. Silverskin onions are pickled in white vinegar, and are much smaller. Full sized onions, e.g. Spanish Onions, can be pickled if sliced first.

In the Southern United States, pickled Vidalia onions can be served as a side dish.

In Hong Kong, pickled onions are served in many Cantonese restaurants, especially around dinner time, as a small dish before the main course is served.

In Switzerland, they are served to accompany raclette, along with pickled gherkins.

In Mexican cuisine, one preparation, cebollas curtidas, has sliced red onions pickled in a mixture of citrus juices and vinegar, which is served as a garnish or condiment. Sometimes cooked beets are added, producing a more strongly pink coloured dish.