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.
Conjunction of celestial bodies is a great support that we have to take advantage of. - Picatrix (Andalusia, ~1000.AD)