He ran flat out to catch the bus.    From Wordnet, Princeton University. 

Adjective : a flat-out effort by all contestants. ,Many of the paintings were flat-out forgeries.    From Dictionary.com. 

Noun : He struck me with the flat of his hand. ,salt flats. ,The flat of B is B flat. ,a juvenile flat.    From Dictionary.com. 

Adverb : flat broke. ,She ran around the track in two minutes flat. ,to sing flat.    From Dictionary.com.