To accumulate or stash away things (money, goods) or intangible things (stress, resentment) over time; to hoard or save up.
給料を毎月少しずつ溜め込んで、旅行のための資金にした。
I saved up a little from my salary every month and used it as travel money.
彼は不満を溜め込むタイプで、ある日突然爆発した。
He tends to bottle up his dissatisfaction, and one day it suddenly exploded.
部屋に物を溜め込むと掃除が大変になる。
If you hoard things in a room, cleaning becomes difficult.
期限ぎりぎりまで資料を溜め込まず、計画的に整理しよう。
Don't leave materials piled up until the last minute; organize them systematically.