demonstrable UK /dɪˈmɒnstɹəbl̩/US /dɪˈmɑnstɹəbl̩/adjective 1noun 1forms 3 adjective1 •Able to be demonstrated.It is easily demonstrable that water extinguishes fire. noun1 •Something that can be demonstrated.We deal here with imponderables rather than demonstrables. — 1949 formsdemonstrables · more demonstrable · most demonstrable