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.
nail n.
Old English negel "tapering metal pin," nægl "fingernail (handnægl), toenail," from Proto-Germanic *naglaz (source also of Old Norse nagl "fingernail," nagli "metal nail;" Old Saxon and Old High German nagel, Old Frisian neil, Middle Dutch naghel, Dutch nagel, German Nagel "fingernail; small metal spike"), from PIE root *(o)nogh "nail of the finger or toe" (source also of Greek onyx "claw, fingernail;" Latin unguis "fingernail, claw;" Old Church Slavonic noga "foot," noguti "fingernail, claw;" Lithuanian naga "hoof," nagutis "fingernail;" Old Irish ingen, Old Welsh eguin "fingernail, claw").
The "fingernail" sense seems to be the original one, but many figurative uses are from the "small metal spike" sense: hard as nails is from 1828. To hit the nail on the head "say or do just the right thing" is by 1520s; in Middle English driven in the nail (c. 1400) was "to drive home one's point, clinch an argument," and smiten the nail on the hed was "tell the exact truth" (mid-15c.). Phrase on the nail "on the spot, exactly" is from 1590s, of obscure origin; OED says it is not certain it belongs to this sense of nail.
As a unit of English cloth measure (about 2 1/4 inches) from late 14c.; perhaps from a nail being used to mark that length on the end of a yardstick.