Obsession
early 16th century (in the sense ‘siege’): from Latin obsessio(n- ), from the verb obsidere (see obsess).
wiktionary
From Latin obsessio(“a besieging”), from obsidere(“to besiege”); see obsess.
etymonline
obsession (n.)
1510s, "action of besieging" (a sense now obsolete), from French obsession and directly from Latin obsessionem (nominative obsessio) "siege, blockade, a blocking up," noun of action from past-participle stem of obsidere "to besiege" (see obsess). Later (c. 1600), "hostile action of an evil spirit" (like possession but without the spirit actually inhabiting the body). Transferred sense of "action of anything which engrosses the mind" is from 1670s. Psychological sense "idea or image that intrudes on the mind of a person against his will" is from 1901.
