This word has been around in its literal sense of an anchor since the sixteenth century. To start with, it usually referred to a rock or big stone that a ship used in lieu of a metal anchor. A fairly modern example is in Jim Davis, by John Masefield: “In the shallow water near the beach, we dropped our killick”.
Nobody seems to know where the word comes from, though it has been argued it’s from the Irish word killech for a wooden anchor (you might think that a wooden anchor would uselessly float, but it actually consists of a wooden frame enclosing a rock, an ancient type of anchor that’s still used in places). The Concise Scots Dictionary, on the other hand, suggests that killick comes from Scots gellock or gavelock for the head of a pickaxe and that the anchor was given that name because a pickaxe is much the same shape as the conventional image of an anchor.
The records show the word has been spelled in so many ways that it was clearly a colloquial or slang term that was passed on mainly in speech. It is now pretty much obsolete in British English, other than as a jargon term in the Navy, though it is known in Australia under the spelling kellick. A leading hand in the Royal Navy is nicknamed that because his badge of rank has a single small anchor on it. Those who know the sea novels of Patrick O’Brian will remember that Captain Aubrey’s steward is called Preserved Killick — no accident.