From Old French 'grosse douzaine' (large dozen), from Late Latin 'grossus' (thick) — and 'grocer' was originally a gross-seller.
A group of 144 items — a dozen dozens — used as a unit of quantity in wholesale trade.
From Middle English 'grosse' (a large quantity, twelve dozen), from Old French 'grosse douzaine' (large dozen, great dozen), from 'gros' (large, thick, coarse), from Late Latin 'grossus' (thick, coarse). The 'gross' was the 'large dozen' — one step up from the regular dozen in the duodecimal counting system used in European commerce. The adjective 'gross' meaning 'total, before deductions' (as in gross income) and 'disgusting' come from the same French source, all sharing the core sense
The word 'grocer' literally means 'a person who sells by the gross.' It comes from Old French 'grossier' (wholesale dealer), from 'gros' (large). A grocer was originally a wholesaler who traded in large quantities — twelve dozen at a time — not the corner shopkeeper of today. The shift from wholesale to retail happened gradually over the sixteenth and seventeenth centuries