The Collaborative International Dictionary
Sneck up
Sneck \Sneck\, v. t. [See Snatch.] To fasten by a hatch; to latch, as a door. [Scot. & Prov. Eng.]
Sneck up, be silent; shut up; hold your peace.
--Shak.
Wiktionary
sneck up
vb. (context obsolete English) Be silent; shut up.