Um and ah verb phrase
Used when one hesitates or does not know what to say next
He kept umming and ahing during his presentation.
He ummed and ahed to speak his mind.
Used to disapprove of someone or something because their ideas, colour, flavor, and character ect. are not firm or clear enough
1. To uncertainly decide to choose between two different people or things
2. To vary between two different conditions or cases
This phrase is formed based on that fact that "Um" and "ah" are frequent filler words that people use out of habit or when they don't know what to say.
To punish someone or something harshly
He's a really strict teacher, so he'll definitely lower the boom on you if you don't do your homework.