I’d say the most popular word in the average parent’s vocabulary would have to be “no.”
To be fair, it’s an important word for moms and dads. Used properly, it creates healthy boundaries for children.
But I think sometimes we over-do our “no’s,” too. We can be a little too protective. Remember Dory, the Pacific blue tang with short-term memory loss from the animated hit “Finding Nemo”? She reminded Marlin, the dad of mis-adventurous Nemo, “You can’t never let anything happen to him.