Furthermore, the double Nuck is when you use both hands up to your big knuckles.
1: a physical act performed by the male partner, immediately preceding sexual intercourse in a rear-entry position.
2: To position one's self to sexually penetrate his partner, specifically in a back-entrance position, otherwise known as 'doggy-style' (common slang).
3: To prepare for copulation.
4: When a stallion (a male horse) positions itself on top of the female horse, just prior to breeding. This pre-penetration act is known as nucking.