This is the 486th most frequent Vietnamese word.
đánh
"Đánh" means "to hit," "to strike," or "to play" (an instrument, game, etc.).
Here, "đánh rơi" means "to drop," where "đánh" is part of the verbal phrase indicating the action of unintentionally letting go.
Tôi đánh rơi điện thoại.
I dropped my phone.
In this usage, "đánh bóng" means "to polish," and "đánh" indicates the act of application or performing the polishing action.
Người thợ đang đánh bóng chiếc xe.
The worker is polishing the car.
"Đánh đàn" means "to play (a musical instrument)," and "đánh" signifies the action of playing or performing.