ETYMOLOGY
from sober + the plural of side
EXAMPLE
“…I am sorry you have been again out of luck with a horse; but do not despair. I have got a sober sides on trial for a week past, but really & truly cannot make time to put him to the proof, & he stands idle in my stable, but hope as I have often, very often hoped before that I shall have more time the next week…”
From: The Selected Letters of Josiah Wedgwood, Feb, 1779
Edited by Anne Finer and George Savage, 1965
Lexicophilia 