At full speed (4,3)
'at full speed' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for flat out that I've seen before include "Exhausted - at full speed" , "At top speed or effort - being horizontal?" , "At top speed; intense (effort)" , "Lying on floor" , "very quickly?" .)
'at full speed' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for amain that I've seen before include "force" , "with violence" , "at great speed" , "powerfully poetic" , "violently" .)