ciertamente
/ˌθjeɾtaˈmente/ · B1 · adv
certainly
👍 cierta + -mente = certain + -ly; cierto shares Latin certus with certain
Spanish forms adverbs by adding -mente to the feminine adjective, the way English adds -ly. Cierto comes from Latin certus, the same root as English certain, so ciertamente lines up piece by piece with certainly.