Definr calls itself an "incredibly fast dictionary," they're not kidding. Definr is a single page, simple-as-possible dictionary lookup tool that delivers results to queries almost instantly (without reloading the page) and suggests words as you type. According to the site, the average lookup time is 14ms and even stayed fast when it was slammed by Digg traffic last weekend. And their server status page said that while I was on the site just now, the average lookup time was under 1ms -- now that's fast.When
The Ruby on Rails-powered site works by caching at least 10,000 definitions in memory (as I write this, that number stands at about 25,000 -- it fluctuates based on load), so that results are delivered nearly instantly. The word completion algorithm, meanwhile, searches about 200,000 words. So to keep that speedy, Definr uses a C module written for Ruby and runs it on its own server. The result, once the Ruby layer is factored in, is that Definr can do 10,000 completions per second without catching its breath.
So why use Definr over more established dictionary sites like Dictionary.com or Merriam Webster? To be honest, you might not. Definr's speed, though impressive, is really more of a gimmick than anything else, and their Firefox search option doesn't work any faster than the Dictionary.com one I already have installed -- and their definitions, based on Princeton's WordNet 2.0, are more barebones. However, their blazing fast word completions do come in handy if you're using the dictionary to check the spelling of a word (which is something I do -- though in the age of spellcheck, I'm not sure how many people use that method).
Useful or not, though, Definr is worth checking out just to marvel at its speed.