There is always some confusion about the difference between keys, cays, and cayos, and yes, while working on Wood’s Chase this morning I went down that rabbit hole. And I’m back to share it with you.
First, they’re all islands and they all mean the same thing.
Keys are found in Florida
Cays are found in the Bahamas and other English speaking islands
Cayos are found in Cuba and other Spanish speaking islands
Grammarist has a basic definition:
A cay is a naturally occurring low island, either a sandbar or a coral reef. Cay is most often applied to Caribbean islands, the preferred pronunciation is “key” Cay comes from the Spanish word, cayo, which means key. Its first use to refer to an island occurred in 1707.
Some further research refined the definition and explains why they are found generally in tropical waters.
Keys, cays, and cayos are found where sediment accumulates on top of a coral reef creating an island. So in this regard, keys are all islands, but all islands are not keys.
I might have stopped there, but I went further into the history of the word.
Some etymologists claim the word dates back to kagh– that meant a wickerwork or a fence. This ancient meaning is reflected in the Gaulish and early French versions of the word.
“The French word was probably originally used with reference to fence-like wooden revetments, which were used to stabilize riverbanks and allow boats to moor,” the OED (Oxford English Dictionary) explains.
When the word first came into English in 1399, the OED says, it was spelled “key” and meant “a man-made bank or landing stage” for ships, either along the water or projecting into it.