Meaning:

• "Una" is the feminine singular form of the indefinite article in Spanish, equivalent to "a" or "an" in English. It is used to refer to an unspecified or non-specific feminine singular noun.

Usage of "Una":

1. As an Article:
   • "Una" is used before a feminine singular noun to indicate one of something in a non-specific manner.
   • Example: Una casa (A house)
2. Gender Agreement:
   • "Una" must match the gender of the noun it modifies. It is only used with feminine singular nouns.
   • Example: Una mujer (A woman)
3. Number Agreement:
   • "Una" is singular, meaning it only refers to one item or person. If you’re referring to more than one, you would use "unas" for feminine plural.
   • Example: Una flor (A flower) vs. Unas flores (Some flowers)
4. Omission:
   • In some phrases, especially with professions or roles, the article "una" may be omitted, particularly after the verb "ser."
   • Example: Ella es doctora. (She is a doctor) instead of Ella es una doctora.

Example Sentences:

1. Una casa (A house):
   • Vivo en una casa pequeña. (I live in a small house.)
2. Una amiga (A friend):
   • Tengo una amiga que vive en España. (I have a friend who lives in Spain.)
3. Una idea (An idea):
   • Tengo una idea interesante. (I have an interesting idea.)
4. Una historia (A story):
   • Ella contó una historia fascinante. (She told a fascinating story.)

Special Cases:

• Before singular feminine nouns that start with a stressed "a" or "ha":
  • Unlike "el" and "la," "una" remains unchanged when it precedes a feminine noun that starts with a stressed "a" or "ha."
  • Example: Una águila (An eagle) remains una because it is feminine. However, in standard usage, it would be un águila for phonetic reasons.

Comparison with "Un":

• "Un": Masculine singular article (e.g., un libro - a book).
• "Una": Feminine singular article (e.g., una flor - a flower).

Summary:

"Una" is used specifically with feminine singular nouns to indicate "a" or "an" in a non-specific sense. It is important to match "una" with feminine nouns and to use it when referring to one item or person.