1.VerbTo make a mock-up or prototype version of something, without some or all off its intended functionality.
"The carpenters dummied up a set of simple props for the rehearsals."
2.VerbTo make a fake version of something; to make a counterfeit.
3.VerbTo suddenly stop talking; shut up; to keep a secret; to refuse to talk.
"When he couldn't think of any more good lies, he just dummied up.; Everyone was discussing the new teacher, but when she entered the room they all dummied up."