'Percussion cap' definitions:

Definition of 'percussion cap'

noun

A detonator that explodes when struck

From: GCIDE

Percussion \Per*cus"sion\ (p[~e]r*k[u^]sh"[u^]n), n. [L. percussio: cf. F. percussion. See Percuss.]
1. The act of percussing, or striking one body against another; forcible collision, esp. such as gives a sound or report. --Sir I. Newton. [1913 Webster]
2. Hence: The effect of violent collision; vibratory shock; impression of sound on the ear. [1913 Webster]
The thunderlike percussion of thy sounds. --Shak. [1913 Webster]
3. (Med.) The act of tapping or striking the surface of the body in order to learn the condition of the parts beneath by the sound emitted or the sensation imparted to the fingers. Percussion is said to be immediate if the blow is directly upon the body; if some intervening substance, as a pleximeter, is, used, it is called mediate. [1913 Webster]
Center of percussion. See under Center.
Percussion bullet, a bullet containing a substance which is exploded by percussion; an explosive bullet.
Percussion cap, a small copper cap or cup, containing fulminating powder, and used with a percussion lock to explode gunpowder.
Percussion fuze. See under Fuze.
Percussion lock, the lock of a gun that is fired by percussion upon fulminating powder.
Percussion match, a match which ignites by percussion.
Percussion powder, powder so composed as to ignite by slight percussion; fulminating powder.
Percussion sieve, Percussion table, a machine for sorting ores by agitation in running water. [1913 Webster]