(as) honest as the day is long American British old-fashioned
If you describe someone as honest as the day is long, you mean that she/he is very honest and reliable.
Jenny is as honest as the day is long in her response.
James is as honest as the day is long, he never cheats on an exam.
He wasn't as honest as the day is long with Mave, though.
To decide to believe someone‘s saying although they may not tell the truth
Used to say that what you're saying is true, or that you'll do what you promise .
trustworthy, stable, unlikely to fail
To be very serious
If someone has a cast iron stomach, they have a strong stomach that can digest unusual food and even bad food without being ill.
Jimmy must have a cast-iron stomach, when he drank milk with lime juice and felt perfectly fine afterward.