trembling vs tremor

trembling and tremor both are nouns.

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

As nouns, tremor is a hyponym of trembling; that is, tremor is a word with a more specific, narrower meaning than trembling:

trembling: a shaky motion
tremor: shaking or trembling (usually resulting from weakness or stress or disease)

Other hyponyms of trembling include tremolo.

trembling (noun)	tremor (noun)
a shaky motion	an involuntary vibration (as if from illness or fear)
	a small earthquake
	shaking or trembling (usually resulting from weakness or stress or disease)

trembling (adjective)	tremor (adjective)
vibrating slightly and irregularly; as e.g. with fear or cold or like the leaves of an aspen in a breeze

trembling (verb)	tremor (verb)
	shake with seismic vibrations