Bandhu means
Srimad-Bhagavatam
SB Canto 4
There are many qualities which indicate a brahminical personality, and it is understood that Ruci followed all the brahminical principles rigidly. Therefore he is specifically mentioned as brahma-varcasvī. One who is born of a brāhmaṇa father but does not act as a brāhmaṇa is called, in Vedic language, a brahma-bandhu, and is calculated to be on the level of śūdras and women. Thus in the Bhāgavatam we find that Mahābhārata was specifically compiled by Vyāsadeva for strī-śūdra-brahma-bandhu (SB 1.4.25). Strī means women, śūdra means the lower class of civilized human society, and brahma-bandhu means persons who are born in the families of brāhmaṇas but do not follow the rules and regulations carefully. All of these three classes are called less intelligent; they have no access to the study of the Vedas, which are specifically meant for persons who have acquired the brahminical qualifications.