Meaning : A grand and imposing entrance (often extended metaphorically).
Example :
The portals of the cathedral.
The portals of heaven.
The portals of success.
Meaning : A site that the owner positions as an entrance to other sites on the internet.
Example :
A portal typically has search engines and free email and chat rooms etc..
Synonyms : portal site
Meaning : A short vein that carries blood into the liver.
Synonyms : hepatic portal vein, portal vein, vena portae