If writing about a specific trade or profession, finding a handbook or guide about it is helpful. For example, a catalog search on the terms "physicians guide" returns books such as this e-book: What if ...? survival guide for physicians published in 2007.
Note: When searching for works on dress in the library catalog, the subject terms often used are "costume" or "fashion."
ARTstor Use the Advanced search form to select Fashion, Costume and Jewelry in the Classification menu to narrow your search to clothing and accessories.
The Costume Institute of the Metropolitan Museum of Art. Includes a collection database. Digital images available.
Fashion Resources: Museums A listing of online fashion collections.
For a more in-depth look into the mind of a person from a particular time or place, try searching the library catalog for autobiographies, memoirs, journals, diaries, correspondence, or narratives (narrow by time – e.g., nineteenth century – and/or place – e.g., France or United States). If you have the name of a specific person, do an author search on that person’s name.
Fore more suggestions on biographies, see Diaries & Memoirs.
There are many free, online slang dictionaries (see this list of dictionaries from Google Directory for some examples). To be on the safe side, it's probably best to check more than one to confirm the meaning of a term!
American English Dialect Recordings The Library of Congress "Center for Applied Linguistics Collection contains 118 hours of recordings documenting North American English dialects."
The Speech Accent Archive is a database of recordings of native and non-native speakers of English from around the world. Produced by the Linguistics Department at George Mason University.
Survey of English Dialects is a database of "288 extracts from the Survey of English Dialects, a groundbreaking nationwide survey of the vernacular speech of England, undertaken by researchers at the University of Leeds." The oldest recordings are from the 1950s and some of the people recorded were born during the 1800s.
International Dialects of English Archive (IDEA) is "free, online archive of primary source dialect and accent recordings for the performing arts."
Looking for recordings in other languages? Try an Internet search on the terms "dialect," "recordings," and the name of the other language (e.g., a Google search on "dialect recordings german").