iterum

iterum is strictly "a second time". It is built on the pronoun stem of is plus the contrastive suffix -terum you can also see in alter, so it says something like "the other time" of two. For "once more" in the open-ended sense of repeatedly, Latin prefers rursus.

That precision is easy to lose in English, where "again" covers both. If you want the open-ended sense, the fixed phrase is iterum atque iterum, "again and again", which piles the word up rather than changing it. The verb itero, "to repeat", comes from it and gives English "iterate" and "reiterate". Despite the look of it, iterum has nothing to do with iter, "journey".