E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
To give one a sneck posset is to slam the door in his face (Cumberland and Westmoreland). The sneck or snick is the latch of a door, and to sneck the door in ones face is to shut a person out. Mrs. Browning speaks of nicking the door.
The lady closed
That door, and nicked the lock.
Aurora Leigh, book vi. line 1,067.
Probably allied to niche, to put the latch into its niche.