Business / Search Engine Optimization (SEO) / Latent Semantic Indexing (LSI): This mouthful just means that the search engines index commonly associated groups of words in a document. SEOs refer to these same groups of words as "Long Tail Searches". The majority of searches consist of three or more words strung together. The significance is that it might be almost impossible to rank well for "mortgage", but fairly easy to rank for "second mortgage to finance monster truck team".
Entertainment / Literature / Semantic Contamination: Change of meaning that occurs when two words sound alike. Because the words are so similar, often the meaning of one becomes attached to the other. This is especially likely with foreign loan words. F MORE
Entertainment / Literature / Semantic Change: A change in what a word or phrase means. MORE