Flat-out (adverb)

Completely and without reservation; without hesitation or reservation; with all one's effort or energy.

Origin:

The phrase "flat-out" is thought to have originated from the early 20th century in the united states, and it is believed that it is a reference to the full-throttle speed of a car, as in a car "driving flat out" with the accelerator pedal pressed all the way to the floor.

Examples:

1. He was flat-out exhausted after running a marathon.
2. She was flat-out lying to me.
3. I'm flat-out determined to finish this project on time.
4. I"m flat-out working on this project, I can"t talk right now.
5. He was flat-out refusing to do it, no matter how much we begged.