to finish; to close; to do something completely; to put away; to put an end to
Example sentences
彼は勉強中に寝入ってしまった。
While he was studying, he fell asleep.
彼は父親からもらった時計をなくしてしまった。
He has lost the watch given by his father.
彼は不注意のため途方もない失策をしてしまった。
As a result of his carelessness, he made a serious blunder.