literary 一~ (a single, one)

The prefix 一 ('one') attached to a noun to mean 'a [single] X' or 'one X' — 一市民 (a citizen), 一読者 (a reader), 一友人 (a friend). Marks an indefinite singular in a slightly bookish or formal register. Conversational Japanese would usually drop the 一 or rephrase with 一人の.