The affix ka is used after the verb graha 'to seize' when the agent so expressed denotes a house.,
Thus ग्रह + क (VI. I. 16) = गृहम् 'a house'. The र is changed into ॠ by the rule of samprasarana. The plural form गृहाः means 'wife', as she is especially the person that constitutes the house; while the plural of गृहं meaning 'house' will be गृहाणि.,