biohazard UK /ˈbaɪəʊˌhæzəd/US /ˈbaɪoʊˌhæzɚd/ noun1 •A biological hazard: a source of risk due to some biological factor such as bacteria or human waste.South Western Railway's Basingstoke station has donated surplus biohazard waste bags to the nearby St Michael's Hospice. — 2020 formsbiohazards