Well, I'm not sure if you are serious or not. because it seems so incredibly obvious to me, but hey, maybe you are.
The word is "natural". Yes, it is spelled the same, but it is pronounced in a Spanish accent. I guess you could say that it is pronounced something like "nah-too-ral" and the "r" is soft.
Naturalesa
cenote
Recorrido por el museo
There's no single Spanish word that is "hardest" but many English speakers have trouble with double r's. This is because a double r is a "rolled" r and it is not a natural English sound
nota natural
The Spanish words for "I have blonde hair" are, "Tengo pelo rubio." The words are pronounced, "TANE-go PAY-low ROO-bee-oh." Sites such as learn-spanish.co.il provide audio pronunciations of many common Spanish words.
The spanish word for guitar is Guitarra. This English word came directly from the Spanish word, but it is not a Spanish word any more than the Spanish word is an Arabic word. "qutar" or a Greek word Chirara.
"De" is the Spanish word for "of".
The spanish word for did is hizo.
The Spanish word for "she" is "ella".
The Spanish word for "in" is "en".
"Con" is the spanish word for "with".
The Spanish word for "who" is "quién".