The dictionary ratifies the persistence of the word. It declares that the meanings of words come from other words. It implies that all words, taken together, form an interlocking structure: interlocking, because all words are defined in terms of other words. This could never have been an issue in an oral culture, where language was barely visible. Only when printing—and the dictionary—put the language into separate relief, as an object to be scrutinized, could anyone develop a sense of word meaning as interdependent and even circular. Words had to be considered as words, representing other words, apart from things. (p. 66)This passage had the unintended effect of moving me farther away from Gleick's views than I was before reading it. It's an old rule to "define" words by using any other words but the one currently being defined, and a synonym for "definition" is "meaning," so it can be easy to think that some correct string of other words is what constitutes the meaning of a word. Gleick carries this to the conclusion that any given word only has meaning by virtue of other words which themselves only have meaning by still more words, or maybe the original word. He considers this as an insight gained through literacy and dictionary making; preliterate people simply weren't in a good position to notice that word meaning arises from a network map of individually meaningless words.
I consider this sort of view an illustrative overreaction to the crude philosophy of language that all words stand directly for things. Gleick would have us believe, instead, that all words stand for words. Not only would this fail to hook up to the world of things, it fails to hook up with the world of ideas. (At least, any ideas which can't be captured by graph theory.) A moderate take is that perhaps some words stand only for words or only for things, but many words stand for ideas. If I want to convey a certain idea to you, I select words intended to evoke that idea — or a similar enough idea — in your mind when you hear my speech or read my writing.
What are dictionary entries under this moderate view? Acts of communication. Dictionary writers are trying to evoke the ideas which are usually intended to be evoked by the use of a word. A good dictionary definition does two things: it correctly identifies the list of commonly-intended ideas behind the use of a word, and it successfully communicates these ideas to dictionary readers. Dictionaries may be artifacts of literate culture, but I would find it very hard to believe everyone waited for dictionaries to be invented before thinking to ask speakers for clarification of strange words. So under the moderate view, an analogue of dictionary use was probably already happening in oral culture. I suspect the major difference in written dictionaries is that authors were expected to define common words, and may have found unexpected challenges in that task.
Gleick, J. (2011). The information: A history, a theory, a flood. New York, NY: Pantheon Books.