This is great! Beats my printed Oxford English Dictionary - and even that doesn't have an entry for Fu Manchu (I wasn't actually searching for this when I discovered it - I'm not researching facial hairstyles or anything, although that's an idea... )
Even though this app is new to Mac users (as of 10.4), the features aren't really any different from the Digital Webster that shipped with every version of NEXTSTEP/OPENSTEP.