The Collaborative International Dictionary of English v.0.48:

antacid \ant*ac"id\ ([a^]nt*[a^]s"[i^]d), antiacid
\an*ti*ac"id\([a^]n*t[-e]*[a^]s"[i^]d), n. [Pref. anti- + acid.]
   (Med.)
   A remedy for neutralizing acidity, especially of the stomach,
   as an alkali or absorbent. -- a. Counteractive of acidity.
   [1913 Webster + AS]

The Collaborative International Dictionary of English v.0.48:

Buffer \Buff"er\ (b[u^]f"[~e]r), n. [Prop a striker. See
   Buffet a blow.]
   1. (Mech.)
      (a) An elastic apparatus or fender, for deadening the jar
          caused by the collision of bodies; as, a buffer at the
          end of a railroad car.
      (b) A pad or cushion forming the end of a fender, which
          receives the blow; -- sometimes called buffing
          apparatus.
          [1913 Webster]

   2. One who polishes with a buff.
      [1913 Webster]

   3. A wheel for buffing; a buff.
      [1913 Webster]

   4. A good-humored, slow-witted fellow; -- usually said of an
      elderly man. [Colloq.] --Dickens.
      [1913 Webster]

   5. (Chem.) a substance or mixture of substances which can
      absorb or neutralize a certain quantity of acid or base
      and thus keep the degree of acidity or alkalinity of a
      solution (as measured by pH) relatively stable. Sometimes
      the term is used in a medical context to mean antacid.
      [PJC]

   6. (Computers) a data storage device or portion of memory
      used to temporarily store input or output data until the
      receiving device is ready to process it.
      [PJC]

   7. any object or person that shields another object or person
      from harm, shock, or annoyance; as, the President's staff
      is his buffer from constant interruptions of his work.
      [PJC]

WordNet (r) 3.0 (2006):

antacid
    adj 1: acting to neutralize acid (especially in the stomach)
    n 1: an agent that counteracts or neutralizes acidity
         (especially in the stomach) [syn: antacid, gastric
         antacid, alkalizer, alkaliser, antiacid]

Moby Thesaurus II by Grady Ward, 1.0:

78 Moby Thesaurus words for "antacid":
   acid, acidity, agent, alexipharmic, alkali, alkalinity, alkalizer,
   alloisomer, anion, annulling, anthelmintic, antibiotic, antidotal,
   antidote, antimicrobial, antipyretic, antitoxic, atom,
   bacteriostatic, base, bicarbonate of soda, biochemical, buffer,
   buffering, calcium carbonate, canceling, cation, chemical,
   chemical element, chromoisomer, compound, copolymer, counteractant,
   counteractive, counteragent, counterbalancing, counterirritant,
   dimer, element, febrifugal, gastric antacid, heavy chemicals,
   high polymer, homopolymer, hydracid, inorganic chemical, ion,
   isomer, macromolecule, magnesia, metamer, molecule, monomer,
   negating, neutralizer, neutralizing, nonacid, nullifier,
   nullifying, offset, offsetting, organic chemical, oxyacid, polymer,
   preventative, preventive, prophylactic, pseudoisomer, radical,
   reagent, remedy, seltzer, sodium bicarbonate, stultifying,
   sulfacid, trimer, vitiating, voiding