Yep Italian for 'proud' The Pegasus emblem came about because one of the original names for the car was Pegasus, and they kept the emblem because they had already released to the public photos of the interior with the pegasus on the horn button.
i thought fiero in Spanish was fire but i guess thats what i get for trying to use a stupid internet translator... yes the real reason they used the name fiero for the car was because it went with the Pegasus in the fact that it meant "proud" and the Pegasus is one of the symbols used with the perceptive meaning of "proud"
It ment proud in Italian in the 80's for Pontiac and in 1968-69 it ment FI rebird a ERO concept for the 1969 for the Firebird Fiero concept show car.
The meaning depends on the year and the car Pontiac applied it to.
The bottom line was it was a name they had registered on a list in late in the cars development and they made it fit their needs. Owning the rights to a name is very improtant as it take time and money to gain the rights for your use.
The car was going to be Pegasus but in the 11th hour Pontiac changed it but not the emblem. On that I have never heard a creditable story of why they changed.