The Collaborative International Dictionary of English v.0.48:

Semantics \Sem*an"tics\, n. sing. or pl. [Gr. shmantikos having
   meaning, from sh^ma a sign.]
   1. the study of the meanings of words and of the sense
      development of words; -- formerly called semasiology.
      [PJC]

   2. a doctrine and philosophical approach to language and its
      relationship to thought and behavior, developed by Alfred
      Korzybski (1879-1950), which holds that the capacity to
      express ideas and thereby improve one's interaction with
      others and one's environment is enhanced by training in
      the more critical use of words and other symbols; -- also
      called general semantics.
      [PJC]

   3. the meanings of words as they are used to achieve an
      effect; especially, the multiple meanings of words or the
      multiplicity of words having the same meaning; -- used in
      referring to the confusion that can be caused
      (intentionally or unintentionally) by multiple meanings;
      as, there's no real difference, it's only a matter of
      semantics.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Semasiology \Se*ma`si*ol"o*gy\, n. [Gr. shmasi`a signification +
   -logy.] (Philol.)
   The science of meanings or sense development (of words); the
   explanation of the development and changes of the meanings of
   words; -- more commonly referred to as semantics. --
   Se*ma`si*o*log"ic*al, a.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

semasiology
    n 1: the branch of semantics that studies the cognitive aspects
         of meaning [syn: cognitive semantics, conceptual
         semantics, semasiology]