Is it permissible to use the word "Rabb" (Lord/Master) to describe a human, as in saying "Rabb al-Usrah" (master of the household), or must its usage be restricted solely to Allah (the Most High)?

There is no religious or linguistic impediment to saying: "So-and-so is the head of the family, or the master of the house," because the word "Rabb" (رب) in the Arabic language can refer to the owner, master, manager, guardian, and benefactor of something. It is not used in its absolute form (unmodified) except for Allah Almighty. As it was mentioned in the noble prophetic Hadith: "until its owner (Rabbaha) finds it." However, "Al-Rabb" (الرب), with the definite article "Al," is one of the names of Allah Almighty and may not be used for anyone other than Him, Glorified be He.