Spiritual Meaning:
Traditionally, the Centaur was half-man and half-beast, and this creature is associated with the Zodiac sign of Sagittarius. It signifies vision  and wisdom.

Psychological / Emotional Perspective:
The symbol of a Centaur in a dream represents our ability to unite two complete opposites in an acceptable way.

Everyday Material Aspects:
To have a Centaur appear in a dream demonstrates the unification of man’s animal nature with his qualities of human virtue and judgement.

Also consult the entry for Fabulous Beasts.