Why is the ninth month called September?
late 14c., from Old French differer (14c.) and directly from Latin differre "to set apart, differ," from dis- "away from" (see dis-) + ferre "carry" (see infer).
Two senses that were present in Latin have gone separate ways in English since c.1500 with defer (transitive) and differ (intransitive). Related: Differed; differing.