According to the OED there are many spellings of 'snath' and it is the pole or shaft of a scythe, as the catalogue link shows. It is a variant of 'snead' but all the forms are irregular and difficult to account for. Of snead, OED says it is 'Old English of obscure origin and not represented in any of the cognate languages'.

So there you are, you really needed to know that I'm sure!