a substance that retards or stops an activity
"The new chemical acts as a potent inhibitor, effectively stopping the rapid growth of bacteria in the contaminated water."
One who or that which inhibits.
"The new chemical compound acts as a potent inhibitor of bacterial growth in the laboratory dish."
In plain English: An inhibitor is something that stops an action from happening or slows it down.
"The new drug acts as an inhibitor to stop viruses from multiplying in your body."
The word inhibitor is formed by adding the suffix "-or" to the verb inhibit. It entered English as a noun meaning one who or something that inhibits an action.