in spanish, there are only masculine and feminine nouns, but they are usually marked by a vowel at or near the end. most masculine nouns end with the vowel "-o", and most feminine nouns end with the vowel "-a". for animate (living) nouns, the gender of the noun is always connected to its biological gender. for example, a male dog is "perro", and a female dog is "perra". if the gender is unknown, the noun is automatically masculine. in plural forms, if at least one of the nouns is male, the plural noun must be masculine, even if most of the members are feminine, like in "the friends" "los amigos". however, if all of the members of a plural noun are female, the plural noun is feminine, as in "las amigas".