Out-and-out

In the sense of completely, totally, thoroughly and is also used as an adjective in the sense of complete or utter, as in an ‘out-and-out’ scoundrel. It dates from the 13th century and derives from the use of ‘out’ as a prefix in words like outdo, outperform etc, where ‘out’ acts as an intensifier in which one completely outdoes or outperforms someone else completely or thoroughly.