I heard the word for the first time when a senpai explained to us in the dorm that we should make sure our laundry won’t be blown off to the neighbor’s house when we hang them out to dry. “Dahil kapag hinangin ang mga labada ninyo, magsu-sumimasen kayo doon sa kabilang bahay.” Clearly, I thought sumimasen meant “excuse me”.
In reality, sumimasen is more a “thank you” expression than “excuse me”, at least by the way I usually use it. When someone does you a favor, you say “sumimasen”. Sumimasen literally means “(it is) not finished (yet)” and comes from the word “sumu” (済む): “to be finished.” And by saying the word, you’re actually telling the other person that the whole affair is not finished yet, and that you would do something to give back the favor that you received.
Sumimasen, one of the most useful words in the Japanese language.