altar - noun - a table or flat-topped rock used in religious ritual
Sorry. I spelled it wrong.
But yeah, the particular definition you quoted was a bit different than the ones I’ve looked up in the past, but makes the same point. The jews used the altAr to offer up sacrifices as a shadow of what was to come - the sacrifice of the body of God in flesh sacrificed for us. The final sacrifice. So one could make the argument that the cross was a type of “altar”. But that is the only thing in a Christian church I feel comfortable calling an altar.