proof: a measure of alcoholic strength expressed as an integer twice the percentage of alcohol present (by volume)
measure: how much there is or how many there are of something that you can quantify
nafcillin: a penicillinase-resistant form of penicillin (trade name Nafcil) used (usually in the form of its sodium salt) to treat infections caused by penicillin-resistant strains of staphylococci