What does Amen mean?

I spoke with Matthew this evening, and he was in good spirits.  He is most ambivalent about the thought of the potential treatment.  I am sure that is to be expected.  I shared a story with him about my daughter, Claire,  He told me to post it here...so here you go.

Claire (age 4) has recently learned both the "Our Father" and the "Hail Mary."  She was proving that she could say them to Evan (her brother, 8) in the car.  She ended the prayer with "Amen."  Evan asked her if she knew what Amen meant.  Her response:  "It means time to go to sleep."  (She says her prayers just before I leave her bedroom at bedtime.)  Evan and I got a kick out of her response.  Evan's explanation to her was..."It means you really mean it."