present participle of decrease
"The number of visitors to the museum is decreasing every day as summer ends."
In plain English: To decrease is to make something smaller, less frequent, or lower over time.
"The population in that area is decreasing every year."
(music) decreasing in tempo and/or volume
"The orchestra began their encore with a slow, fading diminuendo that left the audience breathless."
Decreasing is formed by adding the suffix -ing to the word decrease. This construction indicates the action or process of making something smaller.