This is a really handy website that lets you search all of the Oxford English
dictionary by simply typing your word into
the search field on the top right of the page.
You can also choose to search through all of the articles that have ever been included on the website to find interesting writings from various experts in the many varying word-related fields.
A really handy attribute is the 'Ask the Experts' section. Although this isn't an interactive helpdesk, as it may sound, it is still really useful. It has a lot of questions about the English language that you can navigate fairly easily.
For those of you who use 'US English', you can change the language setting for the whole site to this if you prefer.
Overall, this isn't the prettiest website, but it's still the best of its kind out there and I would highly recommend it for help with your reports, descriptions and to settle arguments on what words mean and how they're spelt!