Green’s Dictionary of Slang

1. (US) a banjo.

1960

(con. c.1930) J. Havoc Early Havoc 47: He swung the banjo over his back [...] ‘Don’t lean too far over the rail with that damn’ plinker hanging around your neck’.

2. an airgun.

1974		Missouri Conservationist XXXV 6: He has had formal gun safety training before going out with his BB plinker.
1988		P. Capstick Last Horizons 234: It is equally superb as a plinker or occasional shooter. [...] Airgun hunting is the perfect microcosm of big-game stalking and shooting.

3. a cheap, low-calibre weapon.

2000

D. Metcalf Shooting Times Mar. 🌐 SIG may be calling its new Hammerli Trailside .22 LR auto pistol a ‘plinker,’ and it may be priced like a ‘plinker,’ but it shoots like a precision match-grade competition gun.

4. one who owns and uses such weapons.

2003

E. Seale ‘Contact Sensors’ on Beam Circuits on Solarbotics.net 🌐 I drew up a similar design for a normally-open sensor, using a spent .22 cal cartridge (if you’re a ‘plinker,’ you should be able to come up with lots of these).