Answer: An emetic
Step-by-step explanation:
Cronus had been swallowing all his children as soon as they were born for he feared that they would overthrow him. His wife however, grew tired of this and hid Zeus. When Zeus eventually came of age, he went back home and disguised himself as the cupbearer of Cronus.
He then put an emetic which was meant to induce vomiting into Cronus's cup and when Cronus drank of it, he vomited Zeus's siblings, his children.