The definition of an aneroid-barometer is an instrument with a needle that moves when a change occurs in atmospheric pressure.
An example of aneroid barometer is what a meteorologist would use to find out if rain is coming.
a barometer with a needle connected by mechanical linkages and springs to a thin, hollow metal disk in which a partial vacuum is maintained: a change in atmospheric pressure changes the shape of the disk, thus moving the needle
A barometer in which variations of atmospheric pressure are indicated by the relative bulges of a thin elastic metal disk covering a partially evacuated chamber.
Expansion or contraction of the vacuum chamber, caused by a change in air pressure, forces the pointer to move.