strong, a strong man, Early Irish balc, strong, Welsh balch, (Stokes). Likely a Celtic bal-ko-, root bal, as in bail. So Ost.; Sanskrit balam, strength ( adhbhal), Greek $$Gbélteros; Wh.St.boliji$$u, greater; Latin debilis.
Etymological dictionary of the Gaelic language.
Alexander Gairm Publications.
1982.