Be in earnest. For example, He really means business with this deadline. This idiom uses business in the sense of “a serious endeavor.” [Mid-1800s]
Words nearby mean business
How to use mean business in a sentence
Her brown-velvet eyes often soothed me, although her eyebrows added to her every demand: “I mean business!”‘Tracing the Blue Light’: Read Chapter 1 of Eileen Cronin’s ‘Mermaid’|Eileen Cronin|April 8, 2014|DAILY BEAST
John Kerry means business, and though their comments were brief, it seems that Livni and Erekat also mean business.The Case For A Less-Guarded Optimism|Emily L. Hauser|July 30, 2013|DAILY BEAST
Death of the I-mean-business-older dude (and subsequent substance abuse).Gossip Girl Deathwatch|Caitlin Shure|February 6, 2009|DAILY BEAST
She'll soon wilt when she sees we mean business—either go, or take a chaperon, or marry the man, whichever she prefers.Ancestors|Gertrude Atherton
I glanced from this Goliath to his little, bird-eyed spouse, and wondered if he had ever tried to mean business with her.The Red One|Jack London
A bill stamp is a thing that often turns up convenient with gents as mean business like Mr. Vavasor and you.Can You Forgive Her?|Anthony Trollope
The first thing I heard Mr. Davis say, was "Damn mean business."
It was equivalent to saying to the officer that the execution of the law was a mean business.