The order of a reaction with respect to ${\mathrm{OH}}^{-}$ is $-1$ The ${\mathrm{OH}}^{-}$ species

An agent known as an inhibitor slows down or obstructs a chemical reaction. b: a chemical that inhibits or lessens the effects of another chemical (such as an enzyme)

The order of a reaction with respect to ${\mathrm{OH}}^{-}$ is $-1$ The ${\mathrm{OH}}^{-}$ species act as an inhibitor.