Why is liquor called spirits?

Alcohol boils at a lower temperature than does water. Thus, with a
still at the properly maintained temp, alcohol evaporates into
'spirits' leaving behind the water and mash. The coil of the still
cools down the vapor causing it to condense into a liquid. Spirits,
ghosts, vapor, mist, etc: all occupy a similar semantic space.

Also consider non scientific reasons.

"Alcohol or drug induced states are an example of this. Why do you
think hard alcohol is called "spirits?" It's because after a certain
level of consumption the alcohol lowers the energetic field of your
personality to where other spirits can enter your body.

When the alcohol wears off and your level of consciousness rises again
the spirit pops out of the body. This is why people report being drunk
and blacking out. They don't remember dancing on the table naked
because their spirit wasn't the one in the body dancing naked. Haven't
you ever seen someone you know act like a totally different person
when they're drunk? Well, this is whats happening.

So you can see how you can easily forget who you truly are while
getting seduced by the daily distractions you face each day. But with
a little conscious effort and focus on what and who matter most in
your life you'll reconnect with the spirit that you are."

http://www.angryenoughtochange.com/articles/personality.html