godan verb (-u), transitive verb
to say (honorific); to deign to say
Originally a respectful verb for a superior's speech; in modern Japanese it is often used sarcastically or humorously to mock someone's pompous or self-important way of speaking. The reading のたもう is an older form.
社長が「今年はボーナスを出す」とのたまった。
The company president deigned to say, 'We'll give out bonuses this year.'
He has the nerve to say, 'I'm a genius.'