I came across a reference to the island of Iona, looked it up, and in that Wikipedia article discovered some startling information about its name (I’ve bolded the startling part):
The earliest forms of the name enabled place-name scholar William J. Watson to show that the name originally meant something like “yew-place”. The element Ivo-, denoting “yew”, occurs in Ogham inscriptions (Iva-cattos [genitive], Iva-geni [genitive]) and in Gaulish names (Ivo-rix, Ivo-magus) and may form the basis of early Gaelic names like Eogan (ogham: Ivo-genos). It is possible that the name is related to the mythological figure, Fer hÍ mac Eogabail, foster-son of Manannan, the forename meaning “man of the yew”.
Mac an Tàilleir (2003) lists the more recent Gaelic names of Ì, Ì Chaluim Chille and Eilean Idhe noting that the first named is “generally lengthened to avoid confusion” to the second, which means “Calum’s (i.e. in latinised form “Columba’s”) Iona” or “island of Calum’s monastery”. The possible confusion results from “ì”, despite its original etymology, becoming a Gaelic noun (now obsolete) meaning simply “island”. Eilean Idhe means “the isle of Iona”, also known as Ì nam ban bòidheach (“the isle of beautiful women”). The modern English name comes from an 18th-century misreading of yet another variant, Ioua, which was either just Adomnán’s attempt to make the Gaelic name fit Latin grammar or else a genuine derivative from Ivova (“yew place”). Ioua’s change to Iona results from a transcription mistake resulting from the similarity of “n” and “u” in Insular Minuscule.
For some reason (probably having to do with my work as an editor) it irritates me when words get changed in this way, whereas ordinary sound change, even via analogy or folk etymology, doesn’t bother me at all. (See this 2003 post for another example, the verb collimate.)