dot: [OE] The underlying meaning of dot seems to be ‘small lump or raised mark’. In Old English (in which there is only a single record of its use) it meant ‘head of a boil’, and it could well be related to English tit ‘nipple’. The word disappears from written texts between the 11th and the 16th centuries, and resurfaces in the sense ‘small lump’. The modern meaning ‘small roundish mark’ does not appear until the 17th century. Dottle ‘unburnt tobacco in the bottom of a pipe’  is a diminutive form of dot. => dottle, tit
Old English dott "speck, head of a boil," perhaps related to Norwegian dot "lump, small knot," Dutch dot "knot, small bunch, wisp," Old High German tutta "nipple;" ultimate origin unclear.
Known from a single source c. 1000; the word reappeared with modern meaning "mark" c. 1530; not common until 18c. Morse telegraph sense is from 1838. On the dot "punctual" is 1909, in reference to a clock dial face. Dot-matrix first attested 1975.