This shouldn't be accepted without looking around a little bit more, but from what I know, the lexical approach is typically applied in psychology as a way of studying the way… humans format language and communicate. The basic idea is that humans store language information in clusters called "lexical chunks." These chunks are phrases with words that are very commonly found together. The word "odor," for example, is defined as the description of a smell, but people typically associate it with a negative smell. That is because odor is usually found in lexical chunks like foul odor, strong odor, disgusting odor, or rank odor. These are all associations that people make when they hear the word "odor." Another example of a lexical chunk is the term "figment of (pronoun) imagination." People rarely use the word figment except in reference to that lexical chunk..
This should be cited because I took the figment example from a site I looked at a week ago: http://www.teachingenglish.org.uk/think/methodology/lexical_approach1.shtml (MORE)