Gracious
Shayn is a modern phonetic spelling variant of the Irish name Shane, which is the Hiberno-English form of John. It ultimately derives from the Hebrew name Yochanan, meaning 'God is gracious'. While rare in this specific spelling, it retains the strong Celtic roots of its predecessors.
Less common today
Shayn isn't in the latest US Top 1000. It last peaked at #3,052 in 1991.
US births per 5-year period, 1990βpresent (SSA data).