Can the Concept of Humidity Be Applied to Non-H20 Molecules?

[Simfish]

So we define humidity as..
"Relative humidity is defined as the amount of water vapor in a sample of air compared to the maximum amount of water vapor the air can hold at any specific temperature in a form of 0 to 100%"

But these definitions of humidity are overly specific to Earth's atmosphere. Is there a more general formulation of the concept that could apply to other molecules? I know that it's related to the statistical distribution of speeds in a group of molecules (and the respective vapor pressure of such molecules if they are found as a liquid under specified temperatures). So if there was enough mercury liquid, could we have a humidity value for mercury? (would saturation values be determined experimentally since theoretical results for all molecules can't always be precise at 2008's lvl of understanding?). And then could we also have dew point values for other molecules like mercury? (or say, methane on Titan's atmosphere, or some other molecule on that of Venus?)

 

[Mapes]

You can divide the partial pressure of any element or molecule by its saturation vapor pressure to determine its effective relative humidity.

You could calculate the "humidity" of mercury even without any liquid present.