underpromise means to promise less than one expects to do.
Among words judged in Lexicurio's Arena, underpromise ranks #435 of 12,827 for Qualifying.
Etymology
From under- + promise.
verb
- To promise less than one expects to do.““He’s wise not to overpromise, but to underpromise and overdeliver,” said Dave Checketts, a former president of the Knicks and then Madison Square Garden who left in 2001 after a power struggle with James L. Dolan, the chairman of the Garden.”