Spontaneously
来自Big Physics
Safin(讨论 | 贡献)2022年4月27日 (三) 19:11的版本 (建立内容为“Category:etymology == google == [https://www.google.com.hk/search?q=spontaneously+etymology&newwindow=1&hl=en ref] mid 17th century: from late Latin spontane…”的新页面)
mid 17th century: from late Latin spontaneus (from ( sua) sponte ‘of (one's) own accord’) + -ous.
wiktionary
spontaneous + -ly