English, via Greek and Latin and the Anglo-Norman Jehan from Hebrew Johanan, "God has been gracious"; NT Matthew 3-4 & Gospel of St John.

Reputedly the most popular boy's name in the English-speaking world, John has given rise to a large number of surnames. There are also very many forename variants in most European languages. Scots families occasionally use boys names for a girl, especially if they were hoping for a boy and wished to honour an ancestor [* see cited memorial inscription below]

In old documents in Latin, the forms Ioannes, Iohannes, Joannes or Johannes may be used, with appropriate case endings.

A correspondent [IS] notes that in Skye, Scotland, Gaelic-speakers use John and Ian/Iain/Eoin interchangeably. In Gaelic areas with a reasonable influx of English speakers, the names might therefore be considered to be synonyms.

Jock, the archetypal nickname for a Scot, is from the Scottish diminutive for John and equivalent to the English pet name Jack.

A further correspondent [Ik] has questioned where the main variants within the British Isles are normally found. This is a summary of what the Oxford Dictionary of Forenames suggests:
- John has some 30-40 variants occurring in most European languages.
- Ian is Scottish and Iain is the Scottish Gaelic spelling.
- Seán [nowadays without the accent] is Irish Gaelic for John via the Anglo-Norman forename Jehan.
- Ieuan is the Welsh version of John and from it comes Iefan. These have been Anglicized as Evan or Ifan, not Ewan/Euan. (These are Scottish Anglicized versions of the Scottish/Irish Gaelic Eóghan [q.v.]. Note, however, that Oxford also suggests that
- Evan is the Scottish Anglicized version of Eghan, but doesn't elaborate on this latter name which has a strong, but possibly coincidental, similarity to Eóghan.

• Note: Another correspondent [LA] has pointed out that many [?most] earlier manuscripts used a common script for capitals "I" & "J". Thus John may have been written and then transcribed as Iohn. Many on-line services have transcribed original documents faithfully so this version might be the one to look for in the indexes to earlier records.

* GB has noted a memorial inscription in Fraserburgh Kirkton Cemetery in Aberdeenshire where two normally male names were given to a baby girl:

"Erected by Christian Buchan in memory of her husband William Buchan … and her daughter John Ann Bruce aged 10 months."