Source : WordNet®

flat out
     adv 1: in a blunt direct manner; "he spoke bluntly"; "he stated his
            opinion flat-out"; "he was criticized roundly" [syn: {bluffly},
             {bluntly}, {brusquely}, {roundly}]
     2: at top speed; "he ran flat out to catch the bus"; "he was
        off down the road like blue murder" [syn: {like blue
        murder}]