flat-out, adv. — Green’s Dictionary of Slang

flat-out adv.

(US)

1. completely, utterly, totally.

1947		P. Newton Wayleggo (1953) 78: We encountered a clutch of young Paradise ducks [...] so after them we went—flat out.
1959		Harvey Air Force 131: He was flat-out scared [HDAS].
1969		N. Cohn Awopbop. (1970) 121: By 1970, she had ceased to storm her songs flat-out. Often she sounded constrained, only half-involved.
1979		‘Iceberg Slim’ Airtight Willie and Me 151: You’re so beautiful and I flat-out adore you.
1981		P. Barton Bastards I Have Known 12: Both flat out like lizards drinking, we were soon neck and neck.
1997		C. Hiaasen Lucky You 201: They flat-out love this guy.
1997		Simon & Burns Corner (1998) 105: A couple of raggedy-ass, dope-eyed black men stumbling through a county shopping center, lifting appliances and we’re flat-out invisible.
2001		‘Randy Everhard’ Tattoo of a Naked Lady 5: Carnies got a word for a crooked game operator like me. They call me ‘Flattie’ cuz I’ll flat-out rob you and make you like it.
2016		Huffington Post 11 June 🌐 Donald Trump flat out lies about Don King’s endorsement.
2020		D. Winslow ‘Sunset’ in Broken 205: Daniels can flat-out surf.

2. openly.

1943		R. Llewellyn None But the Lonely Heart 68: Old Josh said flat out, that morals was what kept you out of going to bed, or coming the acid, with some tart or other.
1945		C.H. Hogan ‘A Yankee ... on Texas Speech’ in AS XX:2 Apr. 82: Texans spend much of their time ‘flat-out telling’ somebody. Thus, ‘I flat-out told him I wasn’t about to carry him down to Santone’ means ‘I told him bluntly nothing could make me give him a lift to San Antonio.’.
1973		in C. Browne Body Shop 147: They tell you flat out how it is.
2001		(con. 1964–8) J. Ellroy Cold Six Thousand 50: She studied his facial scars. He told her flat-out: My best friend put them there.
2021		P. Papathanasiou Stoning 106: ‘We’ve been flat out dealing with the new arrivals’.

In phrases

come flat out with

(orig. US) to state unequivocally, to make one’s point without hesitation.

2002

Katmandu Post 29 Sept. 🌐 The role of the husband was another issue that most girls wanted to stress on. Suruchi Jyoti, 25, from Boston, came flat out with. ‘In this aspect, I am glad that I am westernised. It is only fair that a “male spouse” should contribute to the household duties [etc.].’.