obsession vs anancasm

obsession and anancasm both are nouns.

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

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

obsession: an unhealthy and compulsive preoccupation with something or someone
anancasm: An obsolete term for ritualistic act or sequence of acts performed by a person with obsessive-compulsive neurosis.

obsession (noun)	anancasm (noun)
an unhealthy and compulsive preoccupation with something or someone	An obsolete term for ritualistic act or sequence of acts performed by a person with obsessive-compulsive neurosis.
an irrational motive for performing trivial or repetitive actions, even against your will