Callum derives from the Latin Columba, dove, carried into Gaelic use partly through a revered early saint of that name. The dove gives it a lasting association with peace and gentleness -- calm chosen deliberately, in the way a dove is often read as a symbol of truce rather than passivity.
He that asserts things that can never be proved by experience is deceived and ambitious, but thus it always happens, those that are most ignorant of Art delights to boast of doing things different or wonderful. - Cardan Girolamo (1501-1576)