visual - The etched words - Clue Twenty Six

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The lights dim and you see, behind them, an etching on the wall that you had not noticed previously.

You ponder what the words could mean...

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Answer

I think you are

Calcium Carbonate

A medicine, abbreviated calendar and a cop's criminal with verbal pause;
shortened sugar over retrograte Greek η

η is eta
retrograde makes it "ate", a likely word ending; assume this is charades
over -> on
shortened sugar -> gluc? fruct?

verbal pause is "um" or maybe "uh" or "eh"
cop's criminal -> ?
abbreviated calendar -> cal

Taking the cryptic-clues at face value, it looks like

A medicine [def.]; abbreviated calendar [CAL] + a cop's criminal [???] + verbal pause [UM?] + shortened sugar [GLUC?] + over [ON] + retrograde Greek η [ATE<]
which gives CAL???UM GLUC?ONATE

That's suggestive....

trading out GLUC for CARB - this is definition by example, but ok -
and seeing the obvious missing CI in calcium, give us:

CALCIUM CARBONATE   (A medicine [def.]; abbreviated calendar [CAL] + a cop's criminal [CI]
                    + verbal pause [UM] + shortened sugar [CARB] + over [ON]
                    + retrograde Greek η [ATE<])

Wikipedia tells me a confidential or criminal informant (CI) is a thing, so that answers that too. Yay, learning!