for a moment和for the moment分别是什么意思？

for a moment，“为一片刻”，是指片刻、一会儿或一段简短的时间
简单用法：
wait for a moment 等一会儿
come here for a moment 过来一下

for the moment，“为那时刻”，是指那时、那一刻，带有强调、特指的性质。
简单用法：
wait for the moment to come 等那时刻来临

They have their reasons for keeping their marriage a secret for a moment.
他们有自己的原因，暂时将他们俩的婚姻保守秘密。
点评：这里for a moment可理解为暂时，即短时间的意思。
for a moment是在修饰keepingXXX a secret，这段短语。

They have their reasons for keeping their marriage a secret for the moment.
他们有自己的原因，将他们俩婚姻的那一刻保守秘密。
点评：这里for the moment可理解为某某事件的那一颗，即短时间的意思。不过，全句并不通顺，写成如下较为通顺，但意思又变了。

They have their reasons for keeping their marriage a secret down/solely for the moment.
或
They have their reasons for keeping their marriage a secret till the moment.
(他们有自己的原因，将他们俩婚姻保密到来领的那一刻。)

for a moment 是稍等片刻，过了一会儿
for the moment是在那时，强调某时间点

for a moment是等了一会儿
for the moment是现在