To quell something means to stop it, calm it down, or bring it under control, especially when dealing with disorder, unrest, or strong feelings. When a teacher quells the noise in a classroom, she gets everyone to settle down and focus. When police quell a riot, they restore order and stop the violence.

The word often suggests that whatever's being stopped had real force or energy behind it. You might quell your fear before giving a speech, or quell doubts about whether you can finish a difficult project. A principal might need to quell rumors spreading through the school, or parents might work to quell an argument between siblings before it escalates.

Quell has a sense of firmness to it: it involves actively working to stop or suppress something, rather than waiting for it to fade on its own. When firefighters quell a blaze, they're fighting hard to put it out. When a leader quells an uprising, they're taking decisive action to restore peace. The word suggests both the challenge of what needs stopping and the determination required to stop it.