"self-named, so-called, would-be," 1752 (in Chesterfield), French, from soi "oneself" (from Latin se, see se-) + present participle of dire "to say" (from Latin dicere "speak, tell, say," from PIE root *deik- "to show," also "pronounce solemnly").
software
softy
sog
soggy
Soho
soi-disant
soigne
soil
soiree
sojourn
sojourner