pin down
1．fix by means of a pin；fix immovably用针固定住；压住
They seemed to have pinned his legs down under a heavy weight．他们似乎用很重的东西把他的双腿压得不能动弹了。
2．bind使受约制；使受限制
They managed to pin him down to a particular time and place．他们设法给他规定一个时间和地点。
He agreed to lecture here next year， but I couldn't pin him down to a firm date．他答应明年来讲学，但我无法叫他定出一个具体的日期。
3． get sb． to make a definite statement使表明态度
We did try to pin him down on his plans for the swimming pool，but he remained evasive．我们的确想要他对他所拟订的游泳池计划表明态度，但他总是闪烁其辞。
4． accurately define or determine sth．确定；证实
It was impossible to pin down exactly what it was that he was trying to say．不可能完全弄明白他想说的是什么。
pin one's faith on／upon／to trust 信任
Don't pin your faith on his promises；he is known to be a rogue．不要相信他的诺言，大家都知道他是个无赖。
I shouldn't pin my faith to what he says．我不该盲目相信他的话。