areo-

(Greek: thin, slight, weak; small space)

areometer
A hydrometer; a meter used to determine a fluid's specific gravity.
areometric
1. Of or pertaining to hydrometry (determination of a fluid's specific grqavity by using an aerometer or hydrometer).
areometry
The determination of a fluid's specific gravity by using a hydrometer (a meter used to determine a fluid's specific gravity).