The Collaborative International Dictionary of English v.0.48:

Absorption \Ab*sorp"tion\, n. [L. absorptio, fr. absorbere. See
   Absorb.]
   1. The act or process of absorbing or sucking in anything, or
      of being absorbed and made to disappear; as, the
      absorption of bodies in a whirlpool, the absorption of a
      smaller tribe into a larger.
      [1913 Webster]

   2. (Chem. & Physics) An imbibing or reception by molecular or
      chemical action; as, the absorption of light, heat,
      electricity, etc.
      [1913 Webster]

   3. (Physiol.) In living organisms, the process by which the
      materials of growth and nutrition are absorbed and
      conveyed to the tissues and organs.
      [1913 Webster]

   4. Entire engrossment or occupation of the mind; as,
      absorption in some employment.
      [1913 Webster]

WordNet (r) 3.0 (2006):

absorption
    n 1: (chemistry) a process in which one substance permeates
         another; a fluid permeates or is dissolved by a liquid or
         solid [syn: absorption, soaking up]
    2: (physics) the process in which incident radiated energy is
       retained without reflection or transmission on passing
       through a medium; "the absorption of photons by atoms or
       molecules"
    3: the social process of absorbing one cultural group into
       harmony with another [syn: assimilation, absorption]
    4: the process of absorbing nutrients into the body after
       digestion [syn: assimilation, absorption]
    5: complete attention; intense mental effort [syn:
       concentration, engrossment, absorption, immersion]
    6: the mental state of being preoccupied by something [syn:
       preoccupation, preoccupancy, absorption, engrossment]