An Etymological Dictionary of Astronomy and Astrophysics

The cardinal point which is opposite to north. It is also the direction of the Sun at local noon (in the northern hemisphere).

Etymology (EN): M.E. suth(e), south(e), from
O.E. suth “southward, in the south;” cf. O.S., O.Fris. suth “southward, in the south,” M.Du. suut), O.H.G. sund, perhaps related to base of *sunnon “sun,” with sense of “the region of the sun.”

Etymology (PE): Note: South is related to right since it is to the right when one faces the rising Sun.
This occurs in, for example, in Av., Skt., and O.Ir., as below.

Daštar, from Mid.Pers. dašn “right hand;” Av. dašina- “right;” Ossetic dæsni “skillful, dexterous;” cf. Skt. dáksina- “right; southern;” Gk. dexios («i>*deks-i-uo-) “right,” dexiteros “located on the right side;” L. dexter “right;” Goth. taihswo “right hand;” O.Ir. dess “on the right hand, southern;”

PIE base *deks- “right.” The second element -tar direction suffix, as in Mid.Pers. ošastar “east” (Av. ušastara- “eastern”), dôšastar “west” (Av. daôšatara-, daôšastara- “western”), abâxtar “north” (Av. apāxtara- “northern”), Mod.Pers. bâxtar, → west.