Family History and Genealogy Resources by Surname
Sinclair Surname Origin
A corruption of St. Clair, and that from St. Clara, from the Latin clarus, pure, renowned, illustrious.
Source: An Etymological Dictionary of Family and Christian Names With an Essay on their Derivation and Import; Arthur, William, M.A.; New York, NY: Sheldon, Blake, Bleeker & CO., 1857.
Sinclair Surname Meaning and Family Facts
There is more to Sinclair family history than the origin of your surname:
A Sinclair Family History Thought:
'Every man is his own ancestor, and every man his own heir. He devises his own future, and he inherits his own past.' -- H. F. Hedge