Booby Trap : Phrases
A practical joke. Also a concealed and possibly lethal trap.
Booby has been in use meaning dunce since at least the late 17th century. A 'booby trap' was originally understood to be a practical joke - not necessarily anything dangerous. These two citations from the 19th century indicate that:
Francis Smedley's Frank Fairlegh, or scenes from the life of a private pupil, 1850:
The 1868 Chambers Journal:
This meaning of 'booby trap' is similar to the notion of April Fool, i.e. the joke was such that only a naive 'booby' would fall for it.
By the early 20th century things had got much more serious. By then, traps that could, and were intended to, kill were also called booby traps.