Top deck is a phrase used to describe the highest part of a vessel, usually a boat or a ship. However, there are several other synonyms that can be used to refer to the same part of a boat. Some of the most common synonyms include upper deck, upper level, uppermost deck, upper tier, topmost level, and uppermost tier. These synonyms all refer to the highest part of a ship, and they can be used interchangeably to describe the same part of a vessel. Whether you are writing about boats, ships, or any other vessel, these synonyms will help you to describe the top deck in a variety of ways.