Scottish form of John [q.v.],, from Hebrew "God has been gracious", now in use throughout the English-speaking world. The Gaelic variant Iain is popular in Scottish communities rather than in English ones.
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.