For today’s offering we are once again transported back to the halcyon days of sail, and we are looking at a saying which means to solve a puzzle, to get to the bottom of something.
In ye olde days, many measurements were based on parts of the body – for example the foot was based on the rough or average length of an actual foot. A fathom, which I think was originally used on land as well as at sea, derives from an Anglo-Saxon word which was something like faethm, which literally referred to embracing or outstretched arms, but which in terms of measurement meant the distance between the fingertips of outstretched arms.
The word came to be used almost exclusively by sailors, particularly to measure the depth of water. This might be achieved by lowering a rope weighted at the end till it reached the sea-bottom. The depth was then ascertained by hauling it back in by “arm’s length” sections and counting them – thus, they had fathomed it out!