Son of the grey-haired one
A modern phonetic variant of the English surname Grayson. It traditionally denotes the son of a 'gray' or 'grey' haired man, or the son of a steward (from the Middle English 'greyve').
Less common today
Greysun isn't in the latest US Top 1000. It last peaked at #8,629 in 2018.
US births per 5-year period, 1990βpresent (SSA data).