Many eons ago, when I was an undergraduate student (I exaggerate), a friend of mine introduced me to a nifty little reference application called Atomica. I quickly grew to like the free program, but all too soon after it became a paid-for subscription service, which is a pain when the payment had to be done online and I did not possess a credit card and the disposable income to back it up.
A few days back, I stumbled upon '1-Click Answers' while I was surfing the Web. And just this morning I remembered the name of the program it reminded me of — Atomica.
After a bit of snooping around, I found out that the same guys who brought us Atomica are giving us 1-Click Answers now. See this page for reasons to use Answers.com, the Web site to which the 1-Click application links for the quick searches. Answers.com is an 'Online Encyclopedia, Thesaurus, Dictionary definitions and more'. The service is supported by advertising, which is done in an fairly unobtrusive manner.
Searches are initiated just by holding down the [Alt] key and clicking the word you want to look up.
In case you think it's just me gushing over a silly little program, which I can assure you it is not, see this compilation of testimonials from press sources, including Time Magazine, Forbes.com, C|Net and BusinessWeek.