From Longman Dictionary of Contemporary Englishflat outflat outinformal a) FAST/QUICKas fast as possible Everyone’s working flat out to finish on time. b) American EnglishHONEST in a direct and complete way SYN straight outask/tell somebody flat out She asked him flat out if he was seeing another woman. → flat
Examples from the Corpus
flat out• The exercise involved running flat out for two minutes and then resting for one minute.• O'Leary flat out loves teaching.• Going flat out, the BMW 325 will reach a speed of 140 miles per hour.• They were working flat out to get the job done on time. 