To present participles which come from intransitive verbs, or are themselves employed as adjectives, to mark the absence of the activity, disposition, or condition implied by the participle;

undefended, applied to the gates of a city

lacking electric charge due to a balance of protons and electrons

Material having atoms with the same number of electrons in orbit as the number of protons in the nucleus. Having no electrical charge.

of a particle or body or system; having no charge; "an uncharged particle"; "an uncharged battery"