trembling vs shaky

trembling is a noun but shaky is not a noun.

Word	Noun	Adjective	Verb	Adverb
trembling	Yes	Yes	No	No
shaky	No	Yes	No	No

As adjectives, trembling and shaky are synonyms defined as:

trembling and shaky: vibrating slightly and irregularly; as e.g. with fear or cold or like the leaves of an aspen in a breeze

Other synonyms of trembling include shivering.

trembling (noun)	shaky (noun)
a shaky motion

trembling (adjective)	shaky (adjective)
vibrating slightly and irregularly; as e.g. with fear or cold or like the leaves of an aspen in a breeze	not secure; beset with difficulties
	inclined to shake as from weakness or defect
	vibrating slightly and irregularly; as e.g. with fear or cold or like the leaves of an aspen in a breeze