The Collaborative International Dictionary of English v.0.48:

Infusion \In*fu"sion\, n. [L. infusio a pouring in: cf. F.
   infusion. See Infuse, v. t.]
   1. The act of infusing, pouring in, or instilling;
      instillation; as, the infusion of good principles into the
      mind; the infusion of ardor or zeal.
      [1913 Webster]

            Our language has received innumerable elegancies and
            improvements from that infusion of Hebraisms.
                                                  --Addison.
      [1913 Webster]

   2. That which is infused; suggestion; inspiration.
      [1913 Webster]

            His folly and his wisdom are of his own growth, not
            the echo or infusion of other men.    --Swift.
      [1913 Webster]

   3. The act of plunging or dipping into a fluid; immersion.
      [Obs.] "Baptism by infusion." --Jortin.
      [1913 Webster]

   4. (Pharmacy)
      (a) The act or process of steeping or soaking any
          substance in water in order to extract its active
          principles.
      (b) The liquid extract obtained by this process.
          [1913 Webster]

                Sips meek infusion of a milder herb. --Cowper.
          [1913 Webster]

WordNet (r) 3.0 (2006):

infusion
    n 1: a solution obtained by steeping or soaking a substance
         (usually in water) [syn: infusion, extract]
    2: the process of extracting certain active properties (as a
       drug from a plant) by steeping or soaking (usually in water)
    3: (medicine) the passive introduction of a substance (a fluid
       or drug or electrolyte) into a vein or between tissues (as by
       gravitational force)
    4: the act of infusing or introducing a certain modifying
       element or quality; "the team's continued success is
       attributable to a steady infusion of new talent"

Moby Thesaurus II by Grady Ward, 1.0:

134 Moby Thesaurus words for "infusion":
   absorption and regurgitation, afflatus, affusion, animating spirit,
   animation, animus, aspergation, aspersion, baptism, baptismal gown,
   baptismal regeneration, baptistery, baptizement, brainwashing,
   brewing, catechization, chemical solution, chrismal, christening,
   concentrate, concentration, conditioning, dash, decoction,
   dictation, distillate, distillation, divine afflatus, drench,
   drenching, ducking, dunking, elixir, embedment, enlivenment,
   entrance, essence, exhilaration, expression, extract, extraction,
   fire, firing, font, genius, graft, grafting, hint, imbruement,
   imbuement, immersion, impaction, impactment, implantation,
   impregnation, impression, inculcation, indoctrination, infection,
   infiltration, infixation, infixion, injection, inkling,
   inoculation, insertion, insinuation, inspiration, instillation,
   instillment, interjection, interpenetration, interpolation,
   intimation, introduction, intromission, leach, leachate, leaching,
   lixiviation, lixivium, maceration, marination, mixture,
   moving spirit, penetration, percolation, perfusion, permeation,
   pervasion, pressing, pulping, purification, quintessence,
   refinement, reindoctrination, rendering, rendition, saturation,
   sauce, seasoning, seething, shade, smack, soak, soakage, soaking,
   solution, sopping, soupcon, souse, sousing, spice, spirit,
   sprinkling, squeezing, steeping, suffusion, suggestion, suspicion,
   taint, tempering, tessellation, thought, tinct, tincture, tinge,
   tint, total immersion, touch, trace, transplant, transplantation,
   vestige



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

INFUSION, med. jur. A pharmaceutical operation, which consists in pouring a
hot or cold fluid upon a substance, whose medical properties it is desired
to extract. Infusion is also used for the product of this operation.
Although infusion differs from decoction, (q.v.) they are said to be
ejusdem generis; and in the case of an indictment which charged the prisoner
with giving a decoction, and the evidence was that he had given an infusion,
the difference was held to be immaterial. 8 Camp. R. 74.