The word "obsession" origninates from the Latin word obsessio, meaning "a besieging or blockade,"   It is derived from the past participle of the verb obsidere, which means "to besiege, occupy, or sit opposite to." This Latin root is composed of ob (against) and sedere (to sit). 

The Oxford English Dictionary identifies the earliest evidence of the use of "obsession" in English as being from 1548 in Hall's "Vnion".  The word obsession has a long history in the English Language.  In the1510s it Initially referred to the "action of besieging" (now an obsolete meaning).  Around 1600 the meaning shifted to encompass the "hostile action of an evil spirit."  In the 1670s it gained a more general sense referring to "the action of anything which engrosses the mind,"  The psychological sense of obsession, referring to a persistent, intrusive thought or idea, developed later, around the 1880s, and in 1901 the psychological sense officially emerged, defining it as an "idea or image that intrudes on the mind of a person against his will".  

Examples of "obsession" used in a sentence: 
"He was fascinated by the actress and tracking her every move had become an obsession." 
"She has an obsession about cleanliness."
"Her concern about cleanliness approaches the level of obsession."
"Money has become an obsession for him." 
"An obsession with home ownership is one of the causes of the financial crisis, he says." 
"I've created this love of food that is almost an obsession." 

Examples of other forms of the word, using obsessive and obsessed in a sentence: 
"Many dancers are obsessive about their weight." 
"He is an obsessive workaholic who never stops thinking about his job."
"The new therapy is supposed to help people control their obsessive thoughts. 
"He's obsessed with Taylor Swift and collects anything and everything connected with her." 
"Mankind has always been obsessed by power."
"She is obsessed with personal hygiene."
"The author of the book seems to be obsessed with sexual perversity and death." 

Just the facts:

OBSESSION Definition & Meaning - Merriam-Webster

OBSESSION Synonyms: 53 Similar and Opposite Words | Merriam-Webster Thesaurus