This is the 3748th most frequent Japanese word.
せっけん
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.
お風呂に入る前にはせっけんを準備してください。
Please prepare soap before taking a bath.
The word "せっけん" is used as the material for washing hands.