Citron
A source of confusion is that "citron" or similar words in French (and other languages), and English are false friends, as they refer to the lemon. Indeed, into the 16th century, the English name "citron" included the lemon and perhaps the lime as well.
Gin and tonic
Gin and tonic is traditionally garnished with a slice or wedge of lime, often slightly squeezed into the drink before being placed in the glass. In most parts of the world lime remains the only usual garnish; however, in the United Kingdom it has become common to use lemon as an alternative fruit; use of both fruit together is known as an "Evans". Although the origins of the use of lemons are unknown, their use dates back at least as far as the late 1930s. In addition lemons are often more readily available, and cheaper to purchase, than limes. The use of lemon or lime is a debated issue - some leading brands, such as Gordon's, Tanqueray, and Bombay Sapphire, recommend the use of lime in their gin.