Somebody drew my attention towards the term lukewarm yesterday, wondering why we add the word luke to warm to mean tepid. The term derives from Middle English, first used in the 14th century, when the word ‘luke’ was a adjective meaning tepid or warm. luke derives from leuk, a word first used around 1200, but with an unknown origin.
There are many suggestions for its origin however and there are many clear parallels with other langauges. It has been suggested that leuk may have derived from the word leuk (meaning tepid/weak) in Middle Dutch or Old Frisian, a language spoken on the northern coast of modern Netherlands and Germany before 1500. It could also have come from the Old English term hleowe, meaning warm.
Modern connections are found in the Dutch word lauw, meaning tepid or indifferent, the German lauwarm, meaning lukewarm and the Danish word lunken, meaning half-hearted. Clearly the word derives from the original Proto-Germanic language of Europe.
In English, the use of lukewarm to mean “indifferent” or “lacking in zeal” dates from the 1520s.