demountable adjective 2noun 1forms 3 adjective2 •Able to be removed from its mount; designed to be dismantled. •(old-fashioned) Designed to be removed from the read mechanism. noun1 •(Australia) A temporary and portable building, especially a portable classroom in a school.A whole row of demountables has been abandoned, the window bagged with bright orange plastic. — 1999 formsdemountables · more demountable · most demountable