A germicide is an agent that kills germs.
The word antibiotic contains the two word elements; anti- which means "against," and bio which means "life." (Another word that contains the word element bio- is biology, the study of life or of living organisms.) The word antibiotic therefore means "against life." It was thus named because it kills microorganisms.
Anti-, meaning "against," is a prefix that will help us understand many new words. A few more examples are:
antalgesic - an agent that is "against pain," or a pain-relieving agent
anthelmintic [anti-, against + helminth, L worm] a substance that is against worms
antihistamine - a substance that opposes the action of histamine, a chemical secreted by the body to initiate an inflammatory reaction
anticoagulant - a substance that opposes coagulation or clotting of the blood
If I tell you that gala is the Greek word for "milk," what does antigalactic mean?
It refers to the army of Darth Vadar.
It means you have ants in your milk.
It means you forgot to pasteurize your milk.
It refers to a substance that prevents or decreases the secretion of milk.