two-by-four: a timber measuring (slightly under) 2 inches by 4 inches in cross section
physical entity: an entity that has physical existence
skinheads: a youth subculture that appeared first in England in the late 1960s as a working-class reaction to the hippies; hair was cropped close to the scalp; wore work-shirts and short jeans (supported by suspenders) and heavy red boots; involved in attacks against Asians and football hooliganism