This is the 7204th most frequent Japanese word.
三井
"三井" (Mitsui) is a Japanese surname and also refers to the Mitsui Group, a major corporate conglomerate in Japan.
Here, '三井' refers to Mitsui, a well-known Japanese corporation used as a proper noun to name a specific bank.
三井銀行で口座を開けました。
I opened an account at Mitsui Bank.
In this sentence, '三井' is used as a part of the name for a specific trading company, indicating the organization's identity.
三井商社は世界的に有名です。
Mitsui Trading Company is globally renowned.
Here, '三井' is used to refer to a surname, showing its application in personal names.