Locke's Word Ambiguity

What I found interesting about Locke's discussion has been a common theme in this class: Interpretation of something that we are used to in every day life that can often be overlooked. With Foucault, it was the analysis of the author and what defines them-- something that we may not think about day to day. In the instance of Locke, it was the discussion of words and what exactly they can do: the foundation of discourse. Locke insists that there are exactly two ways that words can be used: to record your own thoughts, and to communicate your thoughts to other people. He also says, however, that words are only arbitrary ideas, which seems contradicting to me. If words are subjective, then how are we supposed to covey our ideas or thoughts to other people? Bizzell/Herzberg's background on Locke even says that he thinks words are ambiguous and that they only refer to ideas. Locke also insists that words are the source of our ideas, which also confused me because I thought he said that words can only communicate or record ideas. I may be reading into this a little too literally, but I find much of Locke's discussion to be contradicting.