[DoctorBeaver (OP)]

Water is. I don't think mercury is. So what does "wet" mean?

[RD]

The verb to wet : to coat with a film of liquid.
The ability of a liquid to wet a surface is inversely proportional to its surface tension.
Water has a high surface tension, so most liquids are "wetter" than water, (e.g. pure alcohol).
Mercury, like water, has an unusually high surface tension.

[lyner]

Adhesion vs cohesive forces, I would suggest. Because of it's high specific heat capacity, once water  has wetted you it also manages to feel very cold. Other wet liquids - like light oils - stick but don't feel as cold.
I don't think there's an official definition.
Mercury wets copper braid very well btw.

[RD]

Mercury reacts with (dissolves) copper ...

Metals such as tin, silver, and copper will form compounds with the mercury.

http://www.madsci.org/posts/archives/2003-04/1049252616.Gb.r.html [Links inactive - To make links active and clickable, login or click here to register]

[DoctorBeaver (OP)]

hmmm, interesting

[lyner]

Water dissolves lots of things - eventually.
I guess dissolving is the ultimate attraction.

[lightarrow]

Mercury reacts with (dissolves) copper ...

Metals such as tin, silver, and copper will form compounds with the mercury.

http://www.madsci.org/posts/archives/2003-04/1049252616.Gb.r.html [Links inactive - To make links active and clickable, login or click here to register]

Ok, but, at room temperature, a mercury drop will first wet a copper surface, then, after xyz days/weeks will have (perhaps) completely dissolved in it. To increase reaction speed you would use fine copper powder. By the way, using fine Cu powder is a way (invented by me and never experimented []) of removing very little Hg drops from pavement after a possible crash of an Hg thermometre.
Maybe gold is even more efficient, but it depends on your budget...  []

[lyner]

Never drop mercury on the floor of an aeroplane - it eats its way through to the outside as the dissolved aluminium oxidises at the mercury air surface.

[Kryptid]

What about when you get down to the molecular level? What if you had a single molecule of water held to a single molecule of sugar by intermolecular forces? Is the molecule of sugar "wet"? If not, then how large does a group of molecules have to be before can be wet?