חֻלְצָה מְכֻפְתֶּרֶת
The Hebrew word for shirt is חֻלְצָה
listen and repeat. And the word for button is כַּפְתּוֹר
listen and repeat.
To form button-down or that which is made with buttons, Hebrew plugs כפתור into the passive-intensive verb form to yield מְכֻפְתָּר
listen and repeat in the masculine and מְכֻפְתֶּרֶת
listen and repeat in the feminine.
אִם אַתָּה לֹא לוֹבֵשׁ חֲלִיפָה, לְפָחוֹת תִּלְבַּשׁ חֻלְצָה מְכֻפְתֶּרֶת!
If you’re not wearing a sports jacket, at least put on a button-down shirt! (to a male)
While I gave examples using the grammatically-correct way of pronouncing these words, you’re more likely to hear Israelis saying מְכֻּפְתָּר
listen and repeat and מְכֻּפְתֶּרֶת
listen and repeat.