Original Definition:
one entrusted with the secrets or confidences of a superior
Example:
"She writ to him discreetly the thoughts of her friend, leting him understand that she was the secretary; that she would serve him in all honest things he could desire." – Francisco de Quintana, The History of Don Fenise, 1651
About the Word:
Many other words that have been formed through the addition of -ary (which comes from the Latin root -arius, meaning 'from') have managed to keep their roots and suffixes neatly tied together: beneficiary, constabulary, and planetary.
So it seems rather obvious, when looking at a word such as secretary, that its original meaning had something to do with secrets. Yet somewhere along the way the word slipped free of its moorings and took on a not terribly secret meaning.
