I. ˈ ̷ ̷| ̷ ̷ adjective
1. chiefly dialect : frank and open : all-out , downright
2. : maximum , top
no technical understanding of driving skill, and anything but flat-out speed is lost on them — Ken Purdy
II. adverb
1. chiefly dialect : bluntly and directly : openly
told him flat-out what I thought
2. : at top speed
III. adverb
: to the greatest degree : completely — usually used as an intensive
is just flat-out confusing