Learn Spanish (Latin America): Encontramos un cuartucho con una tragamonedas; sin embargo, la racha fue mala. - We found a cheap room with a slot machine; however, the streak was bad.

The suffix -ucho is pejorative, meaning it adds a negative, derogatory, or dismissive tone to the original word. By changing cuarto (room) to cuartucho, the speaker isn't just saying it's a small room, but rather a dingy, run-down, or miserable little room (a dump).

Why is tragamonedas feminine here (una tragamonedas), even though compound nouns are usually masculine?

You're right that compound nouns formed by a verb and a plural noun (like el abrelatas or el lavaplatos) are typically masculine. However, tragamonedas (slot machine) is often treated as feminine because it implies the omitted word máquina (una máquina tragamonedas). Both un tragamonedas and una tragamonedas are commonly used in Latin America.

Why do we use fue instead of estuvo for the bad streak (la racha fue mala)?

We use ser (fue) because we are classifying the essential nature of the streak. A racha (streak) isn't a physical object in a temporary state; rather, the event as a whole was a bad one. When evaluating an event or a conceptual period of time as a success or failure, Spanish prefers ser.

Is the word exclusively used for gambling?