riant

The sky of beatific blue, the suns, tiny as children's toys, reflected in all the badges, faces unclouded by the insanity of thoughts [...]: all this was formed of some unique, radiant, riant matter.

--We, by Yevgeny Zamyatin, translated by Bernard Guilbert Guerney in 1960; p. 23 of the 1977 Penguin edition

MW11 says "riant" means "gay" or "mirthful." From Middle French "rire," "to laugh."