The phrase "come up" is a common English idiom used to signify the appearance or occurrence of something unexpected. However, there are a number of synonyms for this expression that can be used to convey the same meaning in a variety of different contexts. Alternatives to "come up" include "arise," "show up," "emerge," "surface," "manifest," "materialize," "pop up," "crop up," and "come to light." Each of these phrases can be employed depending on the specific situation or tone required. For example, "surface" may be more appropriate in a formal context, while "pop up" could be used in a more casual conversation.