The Collaborative International Dictionary of English v.0.48:

Senate \Sen"ate\, n. [OE. senat, F. s['e]nat, fr. L. senatus,
   fr. senex, gen. senis, old, an old man. See Senior, Sir.]
   1. An assembly or council having the highest deliberative and
      legislative functions. Specifically:
      (a) (Anc. Rom.) A body of elders appointed or elected from
          among the nobles of the nation, and having supreme
          legislative authority.
          [1913 Webster]

                The senate was thus the medium through which all
                affairs of the whole government had to pass.
                                                  --Dr. W.
                                                  Smith.
          [1913 Webster]
      (b) The upper and less numerous branch of a legislature in
          various countries, as in France, in the United States,
          in most of the separate States of the United States,
          and in some Swiss cantons.
      (c) In general, a legislative body; a state council; the
          legislative department of government.
          [1913 Webster]

   2. The governing body of the Universities of Cambridge and
      London. [Eng.]
      [1913 Webster]

   3. In some American colleges, a council of elected students,
      presided over by the president of the college, to which
      are referred cases of discipline and matters of general
      concern affecting the students. [U. S.]
      [1913 Webster]

   Senate chamber, a room where a senate meets when it
      transacts business.

   Senate house, a house where a senate meets when it
      transacts business.
      [1913 Webster]

WordNet (r) 3.0 (2006):

senate
    n 1: assembly possessing high legislative powers
    2: the upper house of the United States Congress [syn: United
       States Senate, U.S. Senate, US Senate, Senate]

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "Senate":
   Austria, Barbados, Belgium, Brazil, Canada, Chile, Colombia,
   Dominican Republic, Ecuador, Ethiopia, Fiji, France,
   House of Lords, Iran, Ireland, Italy, Jamaica, Japan, Jordan, Laos,
   Liberia, Malagasy Republic, Malaysia, Mexico, Netherlands,
   Nicaragua, Norway, Paraguay, Philippines, Portugal, Rhodesia,
   South Africa, Swaziland, Switzerland, Trinidad and Tobago, Turkey,
   US, Venezuela, West Germany



Easton's 1897 Bible Dictionary:

Senate
   (Acts 5:21), the "elders of Israel" who formed a component part
   of the Sanhedrin.


Bouvier's Law Dictionary, Revised 6th Ed (1856):

SENATE, government. The less numerous branch of the legislature.
     2. The constitution of the United States, article 1, s. 3, cl. 1,
directs that "the senate of the United States shall be composed of two
senators from each state, chosen by the legislature thereof for six years;
and each senator shall have one vote." The vice president of the United
States," to use the language of the constitution, art. 1, s. 3, cl. 4,
"shall be president of the senate, but shall have no vote unless they be
equally divided." In the senate each state in its political capacity, is
represented, upon a footing of perfect equality, like a congress of
sovereigns or ambassadors, or like an assembly of peers. It is unlike the
house of representatives. where the people are represented. Story, Const.
ch. 10.
     3. The senate of the United States is invested with legislative,
executive and judicial powers.
     4.-1. It is a legislative body whose concurrence is requisite to the
passage of every law. It may originate any bill, except those for raising
revenue, which shall originate in the house of representatives; but the
senate may propose or concur with amendments as on other bills. Const. art.
1, s. 7, el. I.
     5.-2. The senate is invested with executive authority in concluding
treaties and making appointments. Vide President of the United States of
America.
     6.-3. It is invested with judicial power when it is formed into a court
for the trial of impeachments. See Courts of the United States.
     7. In most of the states the less numerous branch of the legislature
bears the title of senate. In such a body the people are represented as well
as in the other house. Vide article Congress; and, for the senates of the
several states, the name of each state. See, also, articles Courts of the
United States, I; House of Representatives; Vice-President of the United
States.



The Devil's Dictionary (1881-1906):

SENATE, n.  A body of elderly gentlemen charged with high duties and
misdemeanors.