How to implement a value alias or synonym

Hi:

v9.0.1 on linux

Is there a way to query on synonyms of a value transparent to the user?
For example, a column called "animal" can have any text value, including 'horse' and 'cow' and 'pig'. But I want the user to find all the animal='pig' records if they specify 'hog' instead.
So..
select * from thetable where animal = 'pig'
..would generate the same results as...
select * from thetable where animal = 'hog'

There are no 'hog' records in the table, just 'pig' records. And I want to have control over the synonyms, perhaps in some sort of ref table ?

Thanks in Advance for any ideas.