B1
to be late so that someone has to wait for you
Dictionary examples:
The printer keeps me waiting so long, I could write it by hand. (0.0)
My computer keeps me waiting so long, I could make coffee. (0.0)
My boss keeps me waiting so often, I should charge him rent. (0.0)
I'm sorry to have kept you waiting. (10.5)
The dentist kept me waiting for a long time. (15.7)