Sl. to chicken out (of something); to get out of something difficult, inconvenient, or dangerous, leaving others to carry the burden. Come on! Don't wimp out now that there's all this work to be done. Ted wimped out on us.
To withdraw from a commitment or course of action because of cowardice or insecurity: I don't want to stand in line for the roller coaster if you're going to wimp out at the last minute.