How are the meanings of words formed?
At the risk of repeating other people's work, we could start by considering Chomsky's thinking on this. Assembled experiences of our senses (touch, hear, smell, feel, hot, cold, etc.) are stored in a cognitive structure. Words (particulary nounds and verbs) are utterances that are associated with bits of the cognitive structure. The association of learned utterances and experiences is maintained in something called 'deep structure', closely associated with the word-less cognitive structure. Rules for assembling sentences are encoded elsewhere, in something called the 'surface structure'. When we want to say something, physical and temporal experiences emerge from the deep structure in the form of noun and verb fragments that are sequenced by the surface structure into linear, arranged sentences. This model explains common experiences and is congruent with some findings in neuroscience. It is also congruent with the theory of neurolinguistic programming (NLP), where words can access or elicit certain subconscious behavior, 'anchor' feelings, and help to discover the communication modalities unique to each human being, supposedly derived from the hyper-complex interplay between surface and deep structures. I don't want to drone on, but I have not heard of any superior theories of semantic and lexical association; I'd love to hear some.