Calvary vs. Cavalry
In the Biblical New Testament, Calvary is the hill where Jesus was crucified. In modern usage, the word’s other definitions are (1) an artistic representation of Christ’s crucifixion, and (2) an ordeal involving great suffering. Cavalry is completely different. It refers to (1) the part of an army that fights on horseback, and (2) a highly mobile modern army unit. Because the only thing separating these two nouns is the placement of the l, they are easily confused.
Calvary is a proper noun (thus capitalized) when it denotes the hill or a work of art. When it denotes a difficult ordeal, it is a common noun and does not need to be capitalized. Ignore what your spell check says. (From the grammarist.com)