Is the word mentira the same in Brazilian and European Portuguese?

No. While the spelling, grammar, and core meaning of "mentira" are identical in both dialects, there are differences in usage and pronunciation. In Brazilian Portuguese, "Mentira!" is frequently used as a standalone interjection to express shock or disbelief (equivalent to "No way!" or "You're kidding!"). In Portugal, while the word is used to denote an untruth, using it as an interjection is much more strictly an accusation of falsehood. Additionally, Brazilian pronunciation is characterized by more open, clear vowels, whereas Continental Portuguese features more closed, reduced, and often "swallowed" vowels.

Brazilian Portuguese Examples

1. Mentira! Eu não vi nada. (No way! I didn't see anything.)
2. Ele contou uma mentira muito grande. (He told a very big lie.)
3. Pare de falar mentira! (Stop lying!)
4. Essa é a maior mentira de todas. (That is the biggest lie of all.)
5. Não acredito nessa mentira. (I don't believe that lie.)

Continental Portuguese Examples

1. A sério? Eu não vi nada. (Really? I didn't see anything.)
2. Ele contou uma mentira enorme. (He told an enormous lie.)
3. Para de dizer mentiras! (Stop telling lies!)
4. Essa é a maior mentira de todas. (That is the biggest lie of all.)
5. Não acredito nessa mentira. (I don't believe that lie.)