Panoply is Greek word for a full set of armor. The Greek word broken down means “all” and “arms.” So it is a full suit of armor including a shield, breastplate, helmet and weapon.
Somewhere along the line the word got changed. Since it mane a completed set of diverse parts or components, it now has a slightly different meaning.
The new meaning of panoply is any complete or impressive collection. Any splendid display is considered a panoply.