IPA: /əˈsɛsɪvli/
KK: /əbˈsɛsɪvli/
In a way that shows excessive preoccupation or fixation on something.
She obsessively checked her phone for messages throughout the meeting.
Obsessively → It is formed from "obsess" (from Latin "obsidere", meaning to sit before or besiege) and the suffix "-ively" (meaning in a manner of). The word "obsessively" describes acting in a manner that is besieged or preoccupied by thoughts or ideas.
Think of being 'besieged' ('obsidere') by thoughts, which helps you remember that 'obsessively' means acting in a way that shows you are preoccupied.