bi ‧ o ‧ weap ‧ on /ˈbaɪəʊwepən $ ˈbaɪoʊ-/ BrE AmE noun [countable]
↑ bacteria or ↑ virus es (=very small living things that cause illness or disease) used as a weapon to kill a lot of people SYN biological weapon :
He warned that influenza could be used as a bioweapon.