When you want to format a single word, do you double-click to select the entire word and then apply the format? If so, you can skip the double-click. Just position the cursor anywhere inside the word and apply the format. There’s no need to select the entire word first. This is particularly helpful if you can apply the formatting via the keyboard, because you don’t have to move your hands from the keyboard to grab the mouse and double-click.
If this doesn’t work for you, chances are someone has unchecked an editing option. Choose Options from the Tools menu and click the Edit tab. Make sure the When Selecting, Automatically Select Entire Word option in the Editing Options section is checked.