"Rattle" can be a noun or a verb.

As a verb, "rattle" means to make a rapid series of short, sharp sounds, often in an irregular manner. For example, a loose windowpane might rattle in the wind, or a car engine might rattle if it's not running smoothly.

As a noun, "rattle" refers to a noisy, rapid series of short, sharp sounds. A baby's rattle is a common example, which is a toy that makes a rattling sound when shaken. "Rattle" can also refer to a tool or device used for making a rattling sound, such as a snake rattle or a percussion instrument like a maraca.

In a figurative sense, "rattle" can also mean to upset or unnerve someone, as in "the unexpected news really rattled her."