"Billy-o" is a colloquialism used to express enthusiasm, excitement, or intensity. Synonyms for this phrase include words like "like crazy," "to the max," and "like mad." Other possible synonyms may include phrases like "with all my might," "going all out," and "with great vigor." These synonyms all share a common sentiment of putting in maximum effort or exhibiting strong emotions. Whether used to describe a person's actions or to indicate their level of excitement, the phrase "billy-o" and its synonyms convey the idea of going above and beyond to achieve a desired outcome.