the study of the formation, meaning, and use of words and of idiomatic combinations of words.
Origin of lexicology
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the study of the overall structure and history of the vocabulary of a language
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Online Etymology Dictionary, © 2010 Douglas Harper