Momentaneously is an adverb that means "for a moment" or "in a moment". However, there are several synonyms for this word that can be used in different contexts. "Momentarily" is a commonly used synonym, but it can also mean "very soon". "Transitorily" and "fleeting" both convey the idea of something being brief or not long-lasting. "Ephemerally" suggests something being short-lived or passing quickly. "Temporarily" implies that something is only for a limited or specified time. "Intermittently" is another synonym that means something happens at irregular intervals or stops and starts repeatedly. Overall, using these synonyms can add variety and clarity to your writing.