dot [OE] The word dot appears only once in Old English manuscripts, meaning ‘the head of a boil’. It then disappears from our records until the late 16th century, when it re-emerges in the sense ‘a small lump or clot’. The sense ‘small mark or spot’ dates from the mid 17th century. In on the dot [L19th], ‘exactly on time’, the dot is one appearing on a clock face to mark the hour. Writers and printers sometimes use a dot in place of a number or letter that they do not know or do not want to specify, and this may be the origin of the year dot [L19th], ‘a very long time ago’—the dot could also be a zero.