This is the 488th most frequent Vietnamese word.
động
"Động" means "move" or "motion" and can also refer to "cave" depending on context.
Here, 'động' is used to mean to stir or to move emotionally.
Trái tim em không hề động trước ánh mắt ấy.
My heart does not stir at that gaze.
In this context, 'động' refers to functioning or operating as part of a verb.
Máy móc trong nhà đã không còn hoạt động.
The machinery in the house is no longer operational.
Here, 'động' refers to a cave as a noun, denoting a natural hollow space in the earth.