1) Possibly 'to chop' or 'to lop off branches'.
A difficult word. The OED has no early examples but Wright offers ‘to chop’ or ‘to lop off branches’ as possible meanings. Those would fit the contexts in which it appears in coal-mining records from the eighteenth century: 1720 14 score and 7 poles sniging out of Tong wood, Farnley
1765 for 100 poles sniging and leading, Tong. It may be a variant spelling of the verb ‘to snag’ which had similar meanings but a much longer history: 1608 Richard Marshall stubbes and snagges wodd in Brandesby oxeclose. A very early by-name takes the connection with wood-cutting back to the fourteenth century: 1339 William Snaghasel, Sowerby.