obsession vs preoccupation

obsession and preoccupation both are nouns.

Word	Noun	Adjective	Verb	Adverb
obsession	Yes	No	No	No
preoccupation	Yes	No	No	No

As nouns, preoccupation is a hypernym of obsession; that is, preoccupation is a word with a broader meaning than obsession:

obsession: an unhealthy and compulsive preoccupation with something or someone
preoccupation: an idea that preoccupies the mind and holds the attention

obsession (noun)	preoccupation (noun)
an unhealthy and compulsive preoccupation with something or someone	the act of taking occupancy before someone else does
an irrational motive for performing trivial or repetitive actions, even against your will	the mental state of being preoccupied by something
	an idea that preoccupies the mind and holds the attention