Words related to *deik-
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.
Old English tacen "sign, symbol, evidence" (related to verb tæcan "show, explain, teach"), from Proto-Germanic *taikna- (source also of Old Saxon tekan, Old Norse teikn "zodiac sign, omen, token," Old Frisian tekan, Middle Dutch teken, Dutch teken, Old High German zeihhan, German zeichen, Gothic taikn "sign, token"), from PIE root *deik- "to show," also "pronounce solemnly."
Meaning "coin-like piece of stamped metal" is first recorded 1590s. Older sense of "evidence" is retained in by the same token (mid-15c.), originally "introducing a corroborating circumstance" [OED].
late 15c., "act of avenging, revenge," from Old French vindicacion "vengeance, revenge" and directly from Latin vindicationem (nominative vindicatio) "act of claiming or avenging," noun of action from past participle stem of vindicare "lay claim to, assert; claim for freedom, set free; protect, defend; avenge" (related to vindicta "revenge"), probably from vim dicare "to show authority," from vim, accusative of vis "force" (see vim) + dicare "to proclaim" (from PIE root *deik- "to show," also "pronounce solemnly," and see diction). Meaning "justification by proof, defense against censure" is attested from 1640s.