This is the 3748th most frequent Japanese word.
せっけん
Soap.
The word "せっけん" is used as the material for washing hands.
せっけんで手を洗いましょう。
Let's wash our hands with soap.
The word "せっけん" refers to soap here used as a subject in describing its fragrance.
そのせっけんはいい香りがします。
That soap has a pleasant fragrance.
The word "せっけん" refers to an object needing preparation for bathing.