As a verb:
* The sun's rays diminish as the day draws to a close. (The sunlight gets weaker)
* Her hopes of winning the race diminished after a bad start. (Her hopes became less likely)
* The loud music diminished as we walked away. (The volume became quieter)
* The company's profits diminished after a poor sales year. (The profits became smaller)
As a noun:
* There was a gradual diminish in the number of visitors. (A decrease in the number)
Other related words:
* Decrease
* Reduce
* Less
* Fewer
* Decline
* Shrink
Antonyms:
* Increase
* Grow
* Expand
* Amplify