Nadsat for the
testicles, or
scrotum, or
bollocks.
The origin of the word appears to be the Russian word yabloko, meaning `apple'.
Best used in the insult
"Come and get one in the yarbles, if ya have any yarbles, you eunuch jelly thou"...
(from Anthony Burgess' novel A Clockwork Orange and expressed perfectly by Malcolm McDowell in Stanley Kubrick's film version)
Infinite thanks to
Frater 219 for additional information.