1.The study of the meanings of words and of the sense development of words; formerly called semasiology.
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.
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.