I don't know if this works with a Microsoft keyboard but, with an Apple keyboard, you can go directly to the Dictionary by placing the cursor in any word then pressing the Control - Command and D keys simultaneously. When that dictionary window is showing, you will see the word Dictionary at the bottom with a down arrow next to it. Click the down arrow and select the Thesaurus.
By the way, if you keep the Control and Command buttons depressed, you can move your cursor from word to word and call up the Dictionary for whatever word you hover over.