Word parts spontaneous + -ly Pronunciation (UK) IPA (key): /spɒnˈteɪ.ni.əs.li/ (US) IPA (key): /spɑnˈteɪ.ni.əs.li/ Adverb Positive spontaneously Comparative more spontaneously Superlative most spontaneously If something happens spontaneously, it happens randomly or suddenly. Wikiwand - on Seamless Wikipedia browsing. On steroids.Remove ads