Spanish feminine nouns starting with a stressed "a" sometimes use masculine articles and quantifiers

In Spanish, the definite article "el" is generally used for masculine nouns and the definite article "la" for feminine nouns. For example:

However there are some feminine nouns in Spanish that use the masculine singular article "el".

Learn about Spanish feminine nouns that use masculine articles

Feminine nouns that start with a stressed "a" (or "ha-") use the masculine singular definite article. With other articles and quantifiers other rules apply.  Here are two examples; both nouns are feminine and start with the letter a but only the one where the stress is on the first syllable takes the masculine singular article el:

With the Artículo definido

For pronunciation reasons, feminine nouns that start with a stressed "a" (or "ha-") take the masculine singular definite article el (not la):

Bear in mind though that when we use these type of nouns in plural with the plural definite article, they do take the feminine one: las (not los) 

This is because there is no pronunciation difficulty when using the feminine plural article.

With the Artículo indefinido

With the indefinite articles un/una (= a singular), although un is more commonly used, una is also acceptable and not considered incorrect.

Both plural articles unos/unas are also acceptable.

Be careful because if there is an adjective between the article and the noun, then everything reverts to the feminine form!

With parts of speech like the Adjetivo demostrativo, the Adjetivo posesivo or the Adjetivo indefinido, their feminine singular and plural form is used. For example:

Here is a list containing some common words that follow this rule:

Feminine words in Spanish that take article "el" instead "la".