casually, casualty

Casually or casually means informally, or happening by chance--
He always looks very proper, even when he is dressed casually.
They dated casually for years, whenever they were both unattached.
Casually or casually also means with indifference or coolness-
He surveyed the scene casually, and tried to hide his boredom.
He referred to her casually, as though he hadn't been searching for her everywhere.

Casualty or casualty is a military term, meaning one of the dead, missing, or wounded--
Their son was a casualty of the last war.
It was nearly impossible to account for every casualty.

Casualty or casualty also describes a insurance against accidents--
You'll want casualty insurance, in case anyone is injured on your property.
Our casualty insurance will pay for the damage to his car, but we don't have property insurance to pay for our own.

Now that you know that, you can say--
"They learned that he was a war casualty two years ago, and now they speak of it casually."

Note--not to be confused with "causality", a physics term meaning the circumstances or conditions that make up cause and effect--
"The temperature drops in both cases, but the causality is different."