Close female friend. According to Digital Underground (ref: 'Good Thing We're Rappin') the phrase is derived from the expression "Nucka" meaning more than simply "my nigga", but transcending this plainly overused phrase to apply to those that are very close friends. The addition of an antecedent "Sh" changes the word to the feminine, meaning "She-Nucka".
What's up, Shnucka?
by Jackie The Mick October 16, 2010