"On the bubble" is a colloquial term that refers to something or someone that is uncertain or on the verge of succeeding or failing. There are many synonyms for this phrase that can be used in different contexts. Some options include "on the brink," "in the balance," "hanging in the balance," "teetering on the edge," "precarious," "doubtful," "uncertain," "undecided," "equivocal," and "unresolved." Depending on the tone and meaning desired, any of these synonyms could be an appropriate substitution for "on the bubble." Whether describing a person's financial situation, a sports team's playoff chances, or the outcome of a decision, these phrases can add variety and nuance to one's vocabulary.