Green’s Dictionary of Slang

1. a car crash.

1978

New Scientist 12 Jan. 90: The equipment is designed to reduce the high incidence of rear-end shunts on motorways.

2. sexual intercourse.

1988		McGill Dict. of Kiwi Sl. 102/2: shunt copulation.
2003		McGill Reed Dict. of N.Z. Sl. [as cit. 1988].