adjective. Of, relating to, or capable of expansion.

Capable of expanding or of expansion; of a nature to expand: as, expansile action.

adjective. Expansible.

adjective. expansionary, relating to expansion

adjective. expandable, which can be expanded

adjective. (of gases) capable of expansion

"Upon this fact the mechanism of respiration mainly depends; and we may see a still further proof of this in the circumstance that, when the thoracic parietes are pierced, so as to let the external air into the cavity of the pleura, the lung collapses and the thoracic side ceases to exert an expansile influence over the lung."

elastic  

expansible