The Collaborative International Dictionary
Telling \Tell"ing\, a. Operating with great effect; effective; as, a telling speech. -- Tell"ing*ly, adv.
Wiktionary
adv. In a telling manner; convincingly.
WordNet
adv. in a telling manner; "the plain manner of its style all the more tellingly points up the horror of the case"
Usage examples of "tellingly".
She wondered why scientists so often couched their views in abstract terms while giving their game away by the tone of voice, seemingly unaware that most people could read their emotions more tellingly than their ideas.
That original appellation was before my time, and I confess to a degree of yearning for an age when bars had, in the main, sensible names, and did not pride themselves on serving their own creakingly-titled cocktails, a Choyce Selection of Our Eftim-able Home-Made Pies, Hotpottes And Other Fyne Dishes, and twenty different designer lagers, all of which taste identical, cost the earth and are advertised on the tellingly desperate Unique Selling Points of having a neat logo, a top that is difficult to open or a bottle neck whose appearance is apparently mysteriously enhanced by having a slice of citrus fruit rammed down it.
As Habermas tellingly points out, they are involved, not in metaphysics (absolutizing A), but metabiology (absolutizing B).