Is that the voice of Apple’s Siri ringing in Google’s ear? It just could be, given that Google (NASDAQ:GOOG) says it’s now working hard to launch a vastly enhanced algorithim based on what’s known as “semantic search.” And that’s pretty much why Apple (NASDAQ:AAPL) and Siri have been getting so much attention lately: Just ask Siri a natural-language question and it offers a similar response.

While not exactly a search engine, Siri is widely seen as a threat to Google’s dominance of the search market. With so many people now using iPhones – you could say, living on iPhones – the ability to get what you’re looking for fast on your smartphone is putting a bit of shiver into Google’s bones.

So it’s fighting back, in a big way. A story in today’s Wall Street Journal describes in great detail the many new aspects Google will be introducing to its iconic search service over the next several months.

The Journal reports that “Amit Singhal, a top Google search executive, said in a recent interview that the search engine will better match search queries with a database containing hundreds of millions of ‘entities’—people, places and things—which the company has quietly amassed in the past two years. Semantic search can help associate different words with one another, such as a company (Google) with its founders (Larry Page and Sergey Brin).”

The semantic enhancements to Google’s search are also a response to Microsoft’s (NASDAQ:MSFT) Bing, which boasts semantic-like contextual search results. In early advertising for Bing, Microsoft described the service as an “answer” engine.

The stakes are obviously enormous for all the players, but especially for Google. As the Journal notes, it currently commands 66% of the search market and fully 75% of all search ad revenue. So anything Google can do to keep pace with – or even pull ahead of – these increasingly capable rivals will have a bottom-line impact.