Countries with the word Guinea in their name

Factual Questions
1

The word Guinea appears in the following countries:

Guinea Republic
Guinea Bissau
French Guinea
Equitorial Guinea
Papua New Guinea

These countries have nothing in common and are located in three separate continents.

It is also a appears in the name of an animal the guinea pig, which is not actually a pig.

What does the word Guinea means and is it is used by the above countries?

2

IIRC some of those are Guiana.

3

An earlier thread on this subject:

http://boards.straightdope.com/sdmb/showthread.php?threadid=11156

Notice the interesting link by Nanobyte. Doesn’t prove anything, but is worth noticing.