Star Trek: The Animated Series
Episode: TAS 22015 - Terratin Incident

When the U.S.S. Enterprise was bombarded by a strange form of radiation on stardate 5577.3 (2269) near the star Cepheus, Spock at first described this energy as harmless "X-waves." But when the entire crew began shrinking as a consequence of this radiation exposure, it quickly became apparent that the harmless "X-waves" were actually highly dangerous spiroid epsilon waves.