NOUN (3)

1. (facetious) a serving of an alcoholic beverage;

2. a serving (of wine) poured out in honor of a deity;

3. the act of pouring a liquid offering (especially wine) as a religious ceremony;

The Collaborative International Dictionary of English v.0.48:

Libation \Li*ba"tion\ (l[-i]*b[=a]"sh[u^]n), n. [L. libatio, fr.
   libare to take a little from anything, to taste, to pour out
   as an offering: cf. F. libation.]
   The act of pouring a liquid or liquor, usually wine, either
   on the ground or on a victim in sacrifice, in honor of some
   deity; also, the wine or liquid thus poured out. --Dryden.
   [1913 Webster]

         A heathen sacrifice or libation to the earth. --Bacon.
   [1913 Webster]

WordNet (r) 3.0 (2006):

libation
    n 1: (facetious) a serving of an alcoholic beverage
    2: a serving (of wine) poured out in honor of a deity
    3: the act of pouring a liquid offering (especially wine) as a
       religious ceremony