— pistonlike , adj.
/pis"teuhn/ , n.
1. a disk or cylindrical part tightly fitting and moving within a cylinder, either to compress or move a fluid collected in the cylinder, as air or water, or to transform energy imparted by a fluid entering or expanding inside the cylinder, as compressed air, explosive gases, or steam, into a rectilinear motion usually transformed into rotary motion by means of a connecting rod.
2. a pumplike valve used to change the pitch in a cornet or the like.
[ 1695-1705; pistone piston, a learned alter. of pestone large PESTLE, equiv. to pest ( are ) to pound (var. of ML pistare, deriv. of L pistus ptp. of pinsere to pound) + -one aug. suffix ]