I searched for "frigid" and it gave me a definition of English word, but the definition is a bit longer, so it collapsed it and displayed "Show more" at the bottom.
Right now I don't think it is possible to expand this with a keyboard alone. Even if I press arrow down to select first answer, then shift+tab, highlight jumps to similar word "cold", there is no way to highlight "show more".
It would be great if there was a keyboard shortcut to expand it, perhaps "q" key that is used to expand quick answer. I don't think it would interfere with it, since it's either quick answer or dictionary word definition.