Self; oneself; by itself.
[Greek autos, self.]
A person writing the story of their own life produces an autobiography; an autocrat retains power in himself; an autodidact is a self-taught person; something or someone autonomous can operate independently; an autopsy, a post-mortem examination, literally means ‘seeing for oneself’ (Greek autoptēs, eyewitness, from optos, seen).
The form often refers to equipment that operates by itself, automatically: an autopilot keeps an aircraft on course without the pilot's intervention; a autofocusing camera focuses without human assistance; automation is the introduction or use of automatic equipment in a factory. An autoclave, a vessel used to sterilize items, was so called because it was self-fastening (either from Latin clavis, key, or clavus, nail, nobody seems sure which).