Origin: Greek prefix micro-
Microbial has 3 different meanings across 1 category:
A microbe or bacterium.
"The microbial community in the soil helped break down organic waste."
Of, relating to, or caused by microbes or microorganisms.
"The patient was treated with antibiotics for a severe microbial infection in her lungs."
In plain English: Microbial means something that is related to tiny living organisms called microbes, such as bacteria and viruses.
"The microbial life in this pond helps keep the water clean."
Usage: This adjective is often confused with the similar-sounding word "microwave," but they have no relation in meaning or usage. It is standardly used in scientific and medical contexts rather than casual conversation.
The word microbial comes from combining microbe with the suffix -ial. It entered English to describe anything relating to or caused by microbes.