introspection vs thoughtfulness

introspection and thoughtfulness both are nouns.

Word	Noun	Adjective	Verb	Adverb
introspection	Yes	No	No	No
thoughtfulness	Yes	No	No	No

As nouns, thoughtfulness is a hypernym of introspection; that is, thoughtfulness is a word with a broader meaning than introspection:

introspection: the contemplation of your own thoughts and desires and conduct
thoughtfulness: a calm, lengthy, intent consideration

Other hypernyms of introspection include contemplation, musing, reflection, reflexion, rumination.

introspection (noun)	thoughtfulness (noun)
the contemplation of your own thoughts and desires and conduct	a considerate and thoughtful act
	the trait of thinking carefully before acting
	kind and considerate regard for others
	a calm, lengthy, intent consideration