an instrumentality invented for a particular purpose
"the device is small enough to wear on your wrist"
"a device intended to conserve water"
something in an artistic work designed to achieve a particular effect
"The director used a sudden change in lighting as a device to emphasize the character's inner turmoil without saying a word."
any ornamental pattern or design (as in embroidery)
"The intricate floral device on her velvet gown caught the light as she turned during the ball."
an emblematic design (especially in heraldry)
"he was recognized by the device on his shield"
Any piece of equipment made for a particular purpose, especially a mechanical or electrical one.
"The new security device at the front gate beeps whenever someone tries to enter without a code."
In plain English: A device is any tool or machine you hold in your hand to do something specific, like a phone or a remote control.
"He used his smartphone to take a photo."
Usage: Use "device" to refer to any tool, machine, or gadget designed to perform a specific function, such as a smartphone or a safety mechanism. It often implies something invented or constructed rather than a natural object or an abstract concept.
The word "device" comes from the Middle English devis, which was borrowed from Old French and originally derived from the Latin dīvīsus, meaning "divided." While it shares a root with the verb "to divide," the noun traveled into English to refer to an invention or contrivance.