That the Cold war was cold is also a joke. It was full, full, full of hot conflicts with client states.
What it seems to have deterred is two major states warring directly.
that was the etymology, given the world we were emerging was one where major world powers came directly to blows amongst themselves rather than through the countless small-scale, regional proxy wars we saw over the 2nd half of the 20th century.
Conventional proxy wars are significantly cooler than all-out thermonuclear war.