Exhaust (5) can be defined as 'DRAIN' (5 letters). It is a verb that means to empty something completely by allowing the contents to flow out. Exhaust is often used in reference to draining a liquid or gas from a container, such as a fuel tank or engine. It can also refer to the act of using up all of a resource, such as energy or time. In this context, it is often used in the phrase 'exhausted all options, ' meaning that all possible solutions have been tried and none have been successful.