1. Explore (casual web searching / keywords)
2. Scholarly conversations (library databases: articles)
3. Support arguments (source citation)
4. Drafts & revisions (librarians & Writing Center)
In addition to the link to Thesaurus.com below, MS Word has a built-in thesaurus:
Fill out the GEOG/BIOL 150 keyword sheet to help you better understand how to create a search string to use in the library search engines.