General purpose:
- Online Etymology Dictionary
- Google Books, set date range and sort by date*
- Google Ngram Viewer
- Bill Mullins has a giant list of Full Text Databases
- Internet Archive
- Project Gutenberg
- HathiTrust Digital Library
- The Right Rhymes: hop-hop slang defined
- Rap Stats by Rap Genius gives an idea of earliest use, but cannot be searched by time
Newspapers:
- USA: Chronicling America (1836-1922) by the Library of Congress
- Australia: Trove (-1954) by the National Library of Australia
- New Zealand: Papers Past (1839-1945) by the Nation Library of New Zealand
Particularly for computing terms:
Google Groups for Usenet archives (also good for slang) (1981 - present)
DSpace@MIT for the CSAIL archives (1959 - present)
IETF's RFC archive (1969 - present)
PDP-10 software archive (~1967 - ~1990), for old source code
Tech Model Railroad Club dictionary, TMRC 1st & 2nd editions (1959, 1960)
The Jargon File and its archives (also here) (1981 - 2003)
MIT's The Tech newspaper archives (1881 - present)
Bitsavers' Software and PDF Document Archive (misc. dates)
* Care must be taken with Google Books' metadata, especially when only a snippet is shown: occasionally the book was published later than the the year Google claims it was, and sometimes they accidentally include multiple books for each record.
Therefore it's important to double check the date: scroll up to confirm the real date for "full view" books, and for preview/"snippet view" verify with another source (such as the Internet Archive, Project Gutenberg or the HathiTrust Digital Library).
