The phrase "on top the world" is a common idiom that describes a feeling of great happiness and success. There are many synonyms for this phrase, each conveying a slightly different connotation. Some of these synonyms include "elated," "thrilled," "overjoyed," "ecstatic," and "exultant." Other synonyms that describe a similar feeling of achievement and satisfaction include "fulfilled," "successful," and "accomplished." Depending on the context, some additional synonyms may include "triumphant," "victorious," or "crowned." Whatever word you choose to use, it is clear that the feeling of being on top of the world is one that is universally celebrated and desired.