1. Having no material form or physical substance.

… The conference committee asked to see the text of Zamenhof’s keynote address. “Through the air of our hall mysterious sounds are travelling,” he had written, “very low sounds, not perceptible by the ear, but audible to every sensitive soul: the sound of something great that is now being born.” He ended with a prayer to the spirit of brotherhood that, under the banner of Esperantism, would unite humankind: “To thee, O powerful incorporeal mystery,” etc.

From the post: The dream of Esperanto bringing about world peace
Source: A language to unite humankind (