before 1000; perhaps to be identified with Old Englishdott head of a boil, though not attested in Middle English; cf. dottle, dit, derivative of Old Englishdyttan to stop up (probably derivative of dott); cognate with Old High Germantutta nipple
Word Origin and History for dot i's and cross one's t's
O.E. dott "speck, head of a boil," perhaps related to tit "nipple." 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.