a person who does not talk
"The shy child sat silently on his father's lap, acting as a perfect dummy during the family photo."
a figure representing the human form
"The actor practiced his new dance routine on a dummy before performing in front of an audience."
a cartridge containing an explosive charge but no bullet
"The bomb disposal team removed the dummy round from the magazine to ensure it wouldn't accidentally fire during transport."
A silent person; a person who does not talk.
"After spending years as a quiet observer, he was often mistaken for a dummy because he rarely said more than a few words at a time."
In plain English: A dummy is an object used to soothe babies by letting them suck on it.
"The toddler dropped his dummy when he saw the puppy running toward him."
Usage: Use the noun form to describe an inanimate object used for testing fit and function before final production begins. Avoid confusing this technical meaning with informal slang referring to a foolish or gullible person.
To make a mock-up or prototype version of something, without some or all off its intended functionality.
"The engineers built a dummy car to test the aerodynamics before installing any engines or wheels."
In plain English: To dummy something means to pretend you are doing it without actually trying your best.
"The new employee quickly dummed in by following her mentor's lead during the first week on the job."
Extremely.
"The dummy test run was so extensive that it simulated every possible failure scenario in extreme detail."
The word dummy comes from the combination of "dumb" and the suffix "-y." It originally referred to a pacifier, specifically describing a nonfunctional replica or teat.