The Hebrew verb luts means to mock, to scoff, or to speak with contempt. The noun form (lets) describes the 'scoffer' or 'mocker' — one of the three character types in Proverbs (alongside the 'simple' and the 'wise').
The scoffer (lets) is one of the most distinctive characters in Proverbs' moral universe. Unlike the simple person who is merely naive, the mocker actively resists wisdom and despises correction: 'Do not rebuke mockers or they will hate you' (Proverbs 9:8). Psalm 1 opens by warning against sitting in 'the seat of mockers (lets).' The scoffer represents the hardened heart that has made contempt a settled disposition. Yet Proverbs promises that when the mocker is punished, 'the simple gain wisdom' — suggesting that even public consequences for luts can serve redemptive purposes for those watching.