Here's why:
* It describes a noun: We use "gentle" to describe something or someone. For example, "a gentle breeze," "a gentle giant," or "a gentle touch."
* It doesn't act or perform an action: "Gentle" doesn't describe an action, unlike a verb.
However, there are some instances where "gentle" can be used as a verb:
* In a figurative sense: You might say, "He gently guided her through the crowd," where "gently" modifies the verb "guided."
* As a command: "Gentle the beast" could be used to mean "Calm the beast," but this usage is uncommon and more poetic.
So, while "gentle" can be used as a verb in rare instances, it's primarily an adjective.