Elmer?

From kb6nu.com

You Learn Something New Every Day

On the Elecraft mailing list, there was some talk about the term “Elmer,” which in amateur radio parlance is someone’s mentor. I thought that the term was of ancient vintage, but apparently, it was coined as recently as 1971.

According to Norm Fusaro, W3IZ, The term first appeared in QST in a March 1971 “How’s DX” column by Rod Newkirk, W9BRD (now also VA3ZBB):

Too frequently one hears a sad story in this little nutshell: ‘Oh, I almost got a ticket, too, but Elmer, W9XYZ, moved away and I kind of lost interest.’ We need those Elmers. All the Elmers, including the ham who took the most time and trouble to give you a push toward your license, are the birds who keep this great game young and fresh.