Old English ta "toe" (plural tan), contraction of *tahe (Mercian tahæ), from Proto-Germanic *taihwō(n) (source also of Old Norse ta, Old Frisian tane, Middle Dutch te, Dutch teen (perhaps originally a plural), Old High German zecha, German Zehe "toe"). Perhaps originally meaning "fingers" as well (many PIE languages still use one word to mean both fingers and toes), and thus from PIE root *deik- "to show."
Þo stode hii I-armed fram heued to þe ton. [Robert of Gloucester, "Chronicle," c. 1300]
The old plural survived regionally into Middle English as tan, ton. To be on (one's) toes "alert, eager" is recorded from 1921. To step on (someone's) toes in the figurative sense "give offense" is from late 14c. Toe-hold "support for the toe of a boot in climbing" is from 1880.