Worsen dial.

or illiterate alteration of WORSE a. and adv. (? arising from the colloq. worse’n = worse than).

1634.  Heywood & Brome, Lancash. Witches, V. i. L 1. It stinket … worsen than ony brimstone.

1854.  Dickens, Hard T., I. xi. From bad to worse, from worse to worsen.

1854.  A. E. Baker, Northampt. Gloss., s.v., It’s worsen than it was.