Definition of pranny in US English:

pranny

noun

British
slang, depreciative
  • Originally: the female genitals. Later: an idiot.

Origin

1940s; earliest use found in Eric Partridge (1894–1979), lexicographer and etymologist. Origin uncertain; perhaps a blend of prat and fanny, or perhaps compare Scots pran to crush, squeeze, compress.

Pronunciation

pranny

/ˈprani/