The Russian word for accordion is гармошка. The accordion is a very popular instrument in traditional Russian culture and is often played at large gatherings such as a wedding свадьба, birthdays день рождения, and many holidays праздники.

My uncle was one of the best accordion players I have ever known. Each time he played the instrument, everyone gathered around him and listened to the beautiful music. I always told my uncle that he played the accordion like a professional and that he would be able to make a very good living by doing so. «Дядя, ты очень хорошо играешь на гармошке. Ты можешь заработать много денег!» “Uncle, you play the accordion very well. You can earn a lot of money!”. During parties, everyone danced and sang as my uncle played the accordion! I remember one time when a few individuals at a party had too much to drink. They danced happily and suddenly, I saw them lose their balance and fall to the ground laughing like hyenas. My mom laughed and said to them «Я думаю что вам пора домой!» “I think it is time for you to go home.” I enjoyed hearing my uncle play the accordion and every time I hear someone play this beautiful instrument, I am reminded of my uncle’s great talent.

Don's additional notes: the other words in Russian for accordion are гармонь (feminine) and гармоника. Аккордеон is specifically a type of accordion with piano-like keys on the right side instead of smaller buttons. You'll also hear about the баян, which is vastly complex version of the instrument. A harmonica in Russian is specifically «губная гармошка» “a mouth accordion.”