IPA: /ˈtɛlɪŋli/
KK: /ˈtɛlɪŋli/
In a way that reveals important information or meaning; in a significant or revealing manner.
She looked at him tellingly, making it clear that she knew more than she was saying.
Tellingly → It is formed from "telling" (from the verb "tell", which comes from Old English "tellan", meaning to count, relate, or narrate) and the suffix "-ly" (meaning in a manner of). The word "tellingly" means in a manner that reveals or indicates something significant.
Think of the act of 'relating' or 'narrating' something ('telling') and how doing it 'in a manner' ('-ly') can reveal important information.