car·ben·i·cil·lin \ˌkär(ˌ)benə̇ˈsilə̇n\noun (-s) Etymology:carb- + benzyl + penicillin : a broad-spectrum semisynthetic penicillin C17H18N2O6S that is effective against gram-negative bacteria (as pseudomonas) and that acts especially by inhibiting cell-wall synthesis