Crossword Genius

Prefix with efficiency (3)

Ross

I believe the answer is:

eco

'prefix with efficiency' is the definition.
(I've seen this in another clue)

This is all the clue.

(Other definitions for eco that I've seen before include "Umberto - - , novelist" , "Green prefix" , "Umberto --, Italian writer" , "Umberto -, Italian author (The Name of the Rose)" , "Environmental group" .)

I've seen this clue in The New York Times and The Chronicle of Higher Education.
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