бо (Tajik) comes from Persian با, from Proto-Iranian *HwáHatah, from Proto-Indo-Iranian HwáHatas, from Proto-Indo-European h₂wéh₁n̥ts, from Proto-Indo-European h₂wḗh₁ti, from Proto-Indo-European h₂weh₁- — to blow.
бо (Tajik): with