1. (使)平静下来;(使)镇定下来
    If you calm down, or if someone calms you down, you become less angry, upset, or excited.

2. (使)平定;平息
    If things calm down, or someone or something calms things down, the amount of activity, trouble, or panic is reduced.

1. become quiet or less intensive

    e.g. the fighting lulled for a moment

    Synonym: lull

2. become quiet or calm, especially after a state of agitation

    e.g. After the fight both men need to cool off.
           It took a while after the baby was born for things to settle down again.

    Synonym: calmcool offchill outsimmer downsettle downcool it

3. make calm or still

    e.g. quiet the dragons of worry and fear

    Synonym: calmquiettranquilizetranquillizetranquillisequietenlullstill