Elmer

In amateur radio culture, an Elmer or elmer is an experienced operator who trains, mentors and otherwise assists new amateurs.

According to the ARRL, the term is a relatively new one, dating back to to the March 1971 issue of QST. In the issue, columnist Rod Newkirk, W9BRD and later VA3ZBB, commented on the importance of mentors in the hobby:

"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."

External link and reference

 * Discussion on the origin of the term at QRZ.com