无防备的英文：
unguard

George has been unfaithful and in a unguarded moment called his wife by his girlfriend's name.
乔治一直对妻子不忠诚，不留心时就会对着妻子叫出其女朋友的名字。

No one knew Hitler better or saw him more often in his unguarded moments than Hess
没有人比赫斯更了解希特勒，赫斯在希特勒公余之暇见到他的次数也最多。