Where to look up words on-line

I used a word that MSWord didn't like the spelling of. I tried looking the word up on-line to verify my spelling and usage (it is not uncommon for MSWord to not like specialized words). My usual lookup site (onelook.com) doesn't like my word either. Search engines such as Google and Norton give me hits for Wiktionary (not a site I place a lot of store in) and a Merriam-Webster link that defines the term but when I click on the link it says it doesn't know the term. They also find lots of documents and websites that use the term (but I'm a believer in GIGO).

What other semi-trustworthy sites are there?