O.n.o. is an abbreviation that is used in many different contexts, and as such, there is not one exact synonym for the term. Depending on the context, synonyms could include words like "one and only," "unique," "exclusive," "solo," "distinctive," "unmatched," "special," and "rare." In the business world, o.n.o. often stands for "or nearest offer," suggesting that the stated price is not necessarily fixed. In other cases, o.n.o. might be short for other phrases, such as "on no account," "one-night-only," or "on name only." It is therefore important to pay attention to context when searching for synonyms for this term.