Archaic term for a woman in a secondary relationship to a man, often in a historical or feudal context. Not used in modern Japanese.
The term 側女房 can be found in documents from the Edo period.
Compound of 側 (そば, 'side') and 女房 (にょうぼう, 'wife' or 'woman'), literally meaning 'side woman'. The exact historical derivation is uncertain, but it reflects a feudal practice of keeping secondary wives or concubines.