From dictionary.com:

1. a wide-ranging and impressive array or display: the dazzling panoply of the maharaja's procession; the panoply of European history.

2. a complete suit of armor.

3. a protective covering.

4. full ceremonial attire or paraphernalia; special dress and equipment.

The word "panoply" derives from a compound Greek word, "pan" = "all" and "hoply," from the "hoplite" or "armed soldier" of ancient times. Hence, the original idea behind the word is that of being "fully (or heavily) armed."