volumenometer

noun
vol·​u·​me·​nom·​e·​ter | \ ˌväl-yə-me-ˈnäm-ət-ər How to pronounce volumenometer (audio) \

Medical Definition of volumenometer

: an instrument for measuring the volume and indirectly the specific gravity of a body (as a solid) by means of the difference in pressure caused by its presence and absence in a closed air space