Posted on 21st August 2015 by melyn Effeythadow is the Cornish word for efficient Yes, efficient in Cornish is effeythadow Share this:Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window) Related Post navigationPrevious post: Ystyn is the Cornish word for extendNext post: Lasnaghus is the Cornish word for teetotal