Find the word definition

Wikipedia
Thunder sheet

A thunder sheet is a thin sheet of metal used to produce sound effects for musical or dramatic events. The device may be shaken, causing it to vibrate, or struck with a mallet. It is also known as a thunder machine, though this can also refer to a large drum used for a similar sound effect.

Thunder sheets are available from some cymbal makers including Paiste and Sabian, or can easily be made out of any scrap metal sheet. If shaken, it is highly recommended that the player wear gloves to prevent cuts on the hands. The thinner and larger the sheet, the louder the sound. The thunder sheet needs to be "warmed up" before the actual sound is desired to be heard. The player(s) will need to start slowly shaking the sheet a few seconds before quickly shaking the sheet.