Idiom: Flat On One's BackCheck definitions of...flatononesbackMeaningsUsed other than figuratively or idiomatically: see flat, on, back.without recourse; helplessA-Z Proximitiesflame upflannelled foolflap one's gumsflash backflat chat flat on one's back flat outflat strapflatten outflavor of the weekflea in one's earSimilar Idiomsflat on one's backback-to-back-to-backflat chatflat outflat strapin nothing flatknock someone flatSimilar Phrasesback-to-backalluvial flatb-flat clarinetbecome flatcold-water flatcommon flat peaflat archflat benchflat bonedouble flatfall flatflat capflat coatflat eartherflat fileflat tireflat-coated retrieverrailroad flatwing flatflat knot