Merriam-Webster
OnLine: Based on the print version of the Merriam-Webster Collegiate
Dictionary, Tenth Edition (1998).
Google:
Type define:your term (ex: define:housing starts). If you don't find it, you
might try typing the word directly into Google. If it's a phrase, be sure to
put double quotation marks around it (ex: "housing starts").
Cambridge Dictionary of American English: This dictionary is
aimed at non-native speakers. Unfortunately, it only searches on the first
word you type in, so you can't search for whole phrases.
ESL resources in MERLOT. Be sure to click the "+" next to
"ESL" to view subcategories as well. The site is hard to use, but the
resources in it are good.