I've looked at the image again and I'm sure that what is recorded is Sell Monger.

However I'm starting to feel ( and there is some offline debate here ) that he was more likely to be a Fell Monger coming from a farming / country background, which was either mis heard or not understood by the Enumerator in the City of Bristol .

Fell Monger-One who removes hair or wool from hides in preparation for leather making

FELLMONGER....Dealer in hides and skins esp. sheep.

Source: Webster's Revised Unabridged Dictionary (1913)

Fellmonger \\Fell"mon`ger\\, n.
A dealer in fells or sheepskins, who separates the wool from
the pelts.