look up any word, like donkey punch:
 
1.
from the highest authority
i'm telling ya, it's true; straight from the horse's mouth!
by zoon June 20, 2005
 
2.
Getting information from the highest authority.

Origin:
When you get a tip for a horse race, the tip is better as nearer it is to the horse e.g. the jockey or the trainer. When you got it straight from the horse's mouth, you have it directly from the source.
This tip is foolproof, I got it (straight) from the horse's mouth!
by TheSunToucher August 12, 2009
 
3.
from the most official source(from the fact that a horse's age can be determined most precisely and directly by examining it's teeth)
He gets his stories straight from the horse's mouth.
by Light Joker July 07, 2005