IPA: /əˈzɜːrvəntli/
KK: /əbˈzɜrvəntli/
In a way that shows careful attention to details or surroundings.
She listened observantly to the instructions given by the teacher.
Observantly → It is formed from "observant" (from Latin "observantem", meaning attentive or watchful) and the suffix "-ly" (meaning in a manner of). The word "observantly" means in a manner that is attentive or watchful.
Think of being 'attentive' ('observant') and doing it 'in a manner' ('-ly'). This helps you remember that 'observantly' means to act in a watchful way.