Word Origin & History
O.E. ta (pl. tan), contraction of *tahe (Mercian tahæ), from P.Gmc. *taikhwo (cf. O.N. ta, O.Fris. tane, M.Du. te, Du. teen, O.H.G. zecha, Ger. Zehe "toe"), probably originally meaning "fingers" as well. Many PIE languages still use one word to mean both fingers and toes. The O.E. plural tan survived
in southwestern England to 14c. The verb meaning "touch or reach with the toes" is first recorded 1813, in expression to toe the mark. This phrase seems to be nautical in origin.
"The chief mate ... marked a line on the deck, brought the two boys up to it, making them 'toe the mark.' " [R.H. Dana, "Two Years Before the Mast," 1840]
Toenail is from 1841. To be on (one's) toes "alert, eager" is recorded from 1921.