The original sense of the word fathom, in Old English, was ‘the enclosure formed by the breast and arms’; fathoms were ‘arms extended in an embrace’, or ‘outstretched arms’. From this the word came to represent a unit of measurement, based on the span of the outstretched arms to the tips of the fingers, later standardized to six feet. Other early units of measurement, such as the ell and the cubit, were similarly based on the length of the arm or forearm.