Symbol (Noun)

Level 1:
Symbol - Símbolo

Easy to see, easy to hear, this is a stereotypical Level 1... Take the English word and add an "-o" to the end and add a small accent difference and you've go the Spanish version.

As you can see in the spelling, the "y" in the English version of the word is replaced by an "í" in the Spanish spelling, "Símbolo." This "í" has a sound almost like a long "E", making the pronunciation much like "SEEM-bo-lo".

Pronounced: "SEEM-bo-lo"

Solution (Noun)

Level 2:
Solution - Solución

This word is almost spelled the same; the difference is a "c" instead of a "t" and an accent on the "o".

This is pronounced "So LOU see-on"

Sentence (Noun)

Level 2:
Sentence - Sentenciar

Okay, so it's not as simple as adding an "-o", but it's just replacing the ending "e" with "-iar" and you've got the Spanish word. Pronounced "Sentence ee are".

The "-iar" ending is pronounced much like in "caviar"

Similar (Adjective)

Level 1:
Similar - Similar

It seems that similar in Spanish is quite similar to similar in English.
While they look identical, the Spanish pronunciation is more like "See-Me-Lar."

Note: Here is a Spanish word that starts with an "S" not "Es."

Stupid (Adjective)

Level 3:
Stupid - Estupido

If you were to add an o to the end, getting "stupido," you would not be using correct Spanish, but a Spanish-speaking person would likely understand you, as the Spanish word for "Stupid" is actually "estupido."

Most words starting in "S" in English that have a very similar counterpart in Spanish start with "Es," instead. Much like Spanish and Espanol.