日积月累的英语单词是"accumulate"，意思是积累、堆积。例如：
The company has accumulated a lot of wealth over the years.
He has been accumulating knowledge and experience in his field for decades.
She has a habit of accumulating clutter in her home.
其他相关短语包括：
Accumulate over time：随着时间的推移而积累
Accumulate gradually：逐渐积累
Accumulate slowly but surely：慢慢但肯定地积累