Definition of "obsess"

obsess

/əbˈsɛs/

verb
third-person singular simple present obsesses, present participle obsessing, simple past and past participle obsessed
1. (passive voice, constructed with "with") To be preoccupied with a single topic or emotion.
  Quotations
  The [Isaac] Newton that emerges from the [unpublished] manuscripts is far from the popular image of a rational practitioner of cold and pure reason. The architect of modern science was himself not very modern. He was obsessed with alchemy.
  2014 June 21, “Magician’s brain”, in The Economist, volume 411, number 8892
  Over the past few months, RAIL has frequently condemned the Department for Transport for its growing contempt for rail customers - by obsessing on cost, caring nothing for service, and not having the slightest interest in growth.
  2023 August 9, Nigel Harris, “Comment: Disinterested and dishonest”, in RAIL, number 989, page 3
2. (transitive) To dominate the thoughts of someone.
3. (intransitive, colloquial, construed with over) To think or talk obsessively about.