Definition from Wiktionary, the free dictionary
troglodyte (plural troglodytes)
- A member of a supposed prehistoric race that lived in caves or holes, a caveman.
- (by extension) Anything that lives underground.
- The cave was populated by albino scorpions, blind salamanders, and other troglodytes.
- A reclusive, reactionary or out-of-date person, especially if brutish.
- The wren, Troglodytes troglodytes.
- (computing) A person who chooses not to keep up-to-date with the latest software and hardware.
Derived terms 
member of a supposed prehistoric race that lived in caves
reclusive or out-of-date person