This article is largely based on an article in the out-of-copyright Encyclopædia Britannica Eleventh Edition, which was produced in 1911. (June 2020)
A panoply is a complete suit of armor. The word represents the ancient Greek πανοπλία (panoplía), where the word πᾶν pân means "all", and ὅπλον hóplon, "arms". Thus panoply refers to the full armor of a hoplite or heavy-armed soldier, i.e. the shield, breastplate, helmet and greaves, together with the sword and lance.
As applied to armor of a later date, panoply did not come into use until the end of the 16th and beginning of the 17th century, and was then used of the complete suits of plate armor covering the whole body.
Because a panoply is a complete set of diverse components, the word panoply has come to refer to any complete or impressive collection.