Grihapati (गृहपति) was a social formation in the time of Panini.
Mention by Panini
V. S. Agrawala  writes about Gṛihapati – The smallest social formation was Gṛiha, its master being called Grihapati (IV.4.90), in whom vested the supreme authority of the family. Generally father was the Grihapati, but after him his eldest son. Sutra IV.1.164 points out that the younger brother was called yuvā, when he was under the guardianship of his elder brother as the head of the family.
The family system was called Gārhapata, of which Panini cites the example of Kuru-Gārhapatam (VI.2.42) i.e. the family system in the Kuru Country, to which Katyayana adds another example, viz., Vriji-Gārhapatam i.e. the family system in the Vriji Country.