ob·sess (əb-sĕs, ŏb-)
v. ob·sessed, ob·sess·ing, ob·sess·es
To preoccupy the mind of (someone) excessively.
To have the mind excessively preoccupied with a single emotion or topic: The conference organizer obsessed over the smallest of details.
[Latin obsidēre, obsess-, to beset, occupy : ob-, on; see OB- + sedēre, to sit; see sed- in the Appendix of Indo-European roots.]
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