Akademik
piston
noun
/ˈpɪstən/
a)
A
solid
disk
or
cylinder
that fits inside a
hollow
cylinder, and moves under
pressure
(
as in
an
engine
) or displaces
fluid
(
as in
a
pump
)
b)
A
valve
device
in some
brass
instruments for changing the
pitch
Wikipedia foundation
.