deterrent UK /dɪˈtɛɹənt/US /dɪˈtɝənt/adjective 1noun 1forms 3 adjective1 •Serving to deter, preventing something from happening. noun1 •Something that deters.Along with trial by ordeal, hanging was the most effective deterrent that could be devised in an age without police or prisons. — 1999 formsdeterrents · more deterrent · most deterrent