to laugh at someone with scorn; to jeer at, deride, or ridicule
This word joins the ordinary verb for laughing (γελάω) to a prefix that turns the laughter against its target. So it never describes friendly or delighted laughter; it always means laughter aimed at someone in order to belittle them. Across a thousand years of Greek writing the sense stays the same: to jeer, to sneer, to laugh a person to scorn.
In the New Testament it appears only three times, and all three are the same moment: the mourners at the house of Jairus laugh at Jesus after he says the dead girl is only sleeping (Matthew 9:24; Mark 5:40; Luke 8:53). The form of the verb pictures ongoing jeering rather than a single burst, which is part of why Jesus clears the room before raising the child.
The Greek Old Testament had used this same word for the way the arrogant deride the poor and the way enemies mock God's faithful. First readers would therefore have heard the mourners' laughter as an act of contempt, standing in sharp contrast to the faith shown by Jairus and by the woman Jesus heals in the same scene.