Is tremble an adjective

Answer 1

Tremble is an action, and therefore a verb.

E.g.

'I felt the Earth tremble as the teacher's anger rose, and steam burst forth from his ears.'

You can use a form of the word 'tremble' to describe something, e.g.

'The trembling student, not knowing the difference between a verb and an adjective, cowered in the corner whilst awaiting his teacher's wrath.'

Here, trembling is still a verb, but because it describes the nature of the student, it also acts as an adjective, so it is called an adverb.