The phrase six-ton can be used to describe an object or entity that weighs six tons, which is equivalent to 12,000 pounds or 5,443 kilograms. However, there are several synonyms that can be used to substitute this descriptive term. These synonyms include "12,000 pounds," "5,443 kilograms," "heavyweight," "enormous," "massive," "burly," and "hulking." These synonyms can be used interchangeably based on the context in which they are used. For instance, if you are describing a vehicle, "heavyweight" or "massive" may be more appropriate, whereas for describing a large animal, "burly" or "hulking" might be more fitting choices.