A combining form, with the meaning of self, one's self, one's own, itself, its own. [1913 Webster]
a prefix with the meaning of self-moving, self-propelling; as, an autocar, an autocarriage, an autotruck, etc., an automobile car, carriage, truck, etc. [Webster 1913 Suppl.]
Auto-, comb. form (usu. aut- before a vowel)
1 self (autism).
2 one's own (autobiography).
3 by oneself or spontaneous (auto-suggestion).
4 by itself or automatic (automobile).