Definition from Wiktionary, the free dictionary
Hacker m (genitive Hackers, plural Hacker)
- (Original, Obsolete.) One whom made an innovative change to MIT's Tech Model Railroad Club hardware.
- extremely skilled individuals that practiced hardcore programming in FORTRAN and other older languages. 
- A person who can optimize/condense computer code to fit into available memory. Ex: My hacker friend condensed my code to fit into a 4k EPROM.
- Someone who gains unauthorized access to a computer, web site, or file.
Declension of Hacker
- Hacker in Duden online
- ^ Steven Levy "Hackers heros of the computer revolution" O'Reilly Media, Inc. (2010) ISBN: 978-1-449-38839-3 page 10