clox·a·cil·lin 
(klŏk′sə-sĭlĭn)
(klŏk′sə-sĭlĭn)n.
A semisynthetic penicillin, C19H18ClN3O5S, that is resistant to penicillinase, used in the form of its sodium salt primarily to treat infections caused by penicillinase-producing staphylococcus bacteria.
[C(H)L(ORO)- + OX(O)- + A(ZO)- + (PENI)CILLIN.]