Armor in the late fifth century bc.

[hoplite14gr]

The Greek word for naked is "Gymnos".
Herodotus calls some Persian troops "Gymnitae".
The term would mean "unarmoured" to his audience or else he would not use it.

But unarmored Greek is "athorakistos" (Th like Thursday) and both Plutrach, Pausanias and Souda lexicon use it.

Kind regards