permissible UK /pəˈmɪsɪbl̩/US /pɚˈmɪsɪbl̩/adjective 2noun 1forms 3 adjective2 •permitted.The units will be allowed to run up to 90 m.p.h. between Chelmsford and Colchester, but their maximum speed of 100 m.p.h. is not permissible on the G.E. line. — 1963 •permissive noun1 •Any tool or device permitted for use in potentially explosive mine environments. formspermissibles · more permissible · most permissible