late O.E. byldan "construct a house," verb form of bold "house," from P.Gmc. *buthlam (cf. O.Fris. bodel "building, house"), from PIE *bhu- "to dwell," from base *bheue- "to be, exist, grow." Rare in O.E.; in M.E. it won out over more common O.E. timbran. Modern spelling is unexplained.
1927, "accumulation of positive publicity," from build + up. Of any accumulation (but especially military) from 1943.