Limey is an old slang

Slang

Slang is the use of informal words and expressions that are not considered standard in the speaker's language or dialect but are considered more acceptable when used socially. Slang is often to be found in areas of the lexicon that refer to things considered taboo...

 nickname, often pejorative

Pejorative

Pejoratives , including name slurs, are words or grammatical forms that connote negativity and express contempt or distaste. A term can be regarded as pejorative in some social groups but not in others, e.g., hacker is a term used for computer criminals as well as quick and clever computer experts...

, for the British

British people

The British are citizens of the United Kingdom, of the Isle of Man, any of the Channel Islands, or of any of the British overseas territories, and their descendants...

, originally referring to their sailor

Sailor

A sailor, mariner, or seaman is a person who navigates water-borne vessels or assists in their operation, maintenance, or service. The term can apply to professional mariners, military personnel, and recreational sailors as well as a plethora of other uses...

s. The term is believed to derive from Lime (fruit)

Lime (fruit)

Lime is a term referring to a number of different citrus fruits, both species and hybrids, which are typically round, green to yellow in color, 3–6 cm in diameter, and containing sour and acidic pulp. Limes are a good source of vitamin C. Limes are often used to accent the flavors of foods and...

, referring to the Royal Navy

Royal Navy

The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

 and Merchant Navy

Merchant Navy

The Merchant Navy is the maritime register of the United Kingdom, and describes the seagoing commercial interests of UK-registered ships and their crews. Merchant Navy vessels fly the Red Ensign and are regulated by the Maritime and Coastguard Agency...

 practice of supplying lime juice to British sailors to prevent scurvy

Scurvy

Scurvy is a disease resulting from a deficiency of vitamin C, which is required for the synthesis of collagen in humans. The chemical name for vitamin C, ascorbic acid, is derived from the Latin name of scurvy, scorbutus, which also provides the adjective scorbutic...

. The benefits of citrus

Citrus

Citrus is a common term and genus of flowering plants in the rue family, Rutaceae. Citrus is believed to have originated in the part of Southeast Asia bordered by Northeastern India, Myanmar and the Yunnan province of China...

 juice were well known at the time thanks to the acute observations of surgeon James Lind

James Lind

James Lind FRSE FRCPE was a Scottish physician. He was a pioneer of naval hygiene in the Royal Navy. By conducting the first ever clinical trial, he developed the theory that citrus fruits cured scurvy...

 who studied the effects of citrus on scurvy in 1747.

Limes replaced lemon

Lemon

The lemon is both a small evergreen tree native to Asia, and the tree's ellipsoidal yellow fruit. The fruit is used for culinary and non-culinary purposes throughout the world – primarily for its juice, though the pulp and rind are also used, mainly in cooking and baking...

s because limes were more readily available from Britain's own Caribbean

Caribbean

The Caribbean is a crescent-shaped group of islands more than 2,000 miles long separating the Gulf of Mexico and the Caribbean Sea, to the west and south, from the Atlantic Ocean, to the east and north...

colonies. Lemon juice was reintroduced after scurvy again became a problem because of lime juice lacking sufficient vitamin C.

The term is thought to have originated in the Caribbean in the 1870s. A false etymology is that it is a derivative of "Cor-blimey" ("God blind me!" or "God blight me!").