Gruner is a simplification of "Grüner Veltliner" (correct English spelling: Gruener Veltliner)- a grape variety grown widely in Austria; the local wine-makers produce all kind of wines from this grape, from the greatest examples of world class quality to simply wines for everyday drinking and even for mixing with mineral water. The popularity of "Gruener" (!) is steadily growing in the USA, even more in GB.
I´ve tasted a marvallous Gruner (correct: Gruener) yesterday.
Gruners are the little, spoke-like, grooves that make up the butthole or anus.
"That cat needs to lick it's ass again, it still has shit stuck all up in it's GRUNERS"