Brain – el cerebro
To remember that brain is pronounced theh-reh-bro (cerebro) in European Spanish, use the following mnemonic:
His brain was hurting after the difficult exam he'd sat that day, then his friend said, 'Look at the ray, bro!' (celebro), and he felt a lot better.
Cerebro is masculine, so it's el cerebro. Imagine a brain that looks like an elephant.