One of the mysteries of the English language finally explained.
Definition of south side in English:
south side
noun
The southern part or side of something; the south; specifically the southern part of a region or city.
adjective
Of, belonging, or relating to the southern part of a place, country, or region.
Origin
Middle English; earliest use found in The Chronicle of Robert of Gloucester. From south and side. Compare Old Frisian sūthasīde, sūthsīde, Middle Dutch suutside, zuutzide (Dutch zuidzijde), Middle Low German sǖtsīde.