Learn Hardcore Italian: Nel canyon sento un'eco forte dopo ogni parola che pronuncio. - In the canyon I hear a loud echo after every word I say.

In Italian, when una comes before a feminine noun starting with a vowel (like eco), the a is dropped and replaced with an apostrophe for euphony. So una eco becomes un’eco.

How do I know that eco is feminine, even though it ends in -o?

Most Italian nouns ending in -o are masculine, but there are exceptions you must memorize. Eco is one of those exceptions and is always feminine: l’eco, un’eco, le eco, due echi.

Why is eco singular here, when it seems there are echoes after every word?

Each time you speak a word you hear one echo. You’re describing the echo that follows each individual word, so you use the singular. If you wanted to talk about multiple echoes at once, you’d say echi forti.

Why does the adjective forte come after eco, and why doesn’t it change ending for feminine?

Adjectives in Italian usually follow the noun. Forte ends in -e, so it has the same form for both masculine and feminine singular. Its plural would be forti.