From Vol. IX Part II of the Oxford English Dictionary (1st edition), published 1919, page 1.

Su‧antly, adv. Now dial. [f. prec. + -LY2.] Regularly, evenly, uniformly, smoothly.

The form sewantly of quot. 1592-3 was entered in Kersey's ed. of Phillips World of Words (1706) as sevantly with def. 'well, honestly'. Some mod. dicts. have copied this and have further invented a form sevant adj.

1547 RECORDE Judic. Uryne i8b, Not suantly and uniformly joyned together. 1592-3 Act 35 Eliz. c. 10 § i That eche sorte of the saide Kersyes or Dorens shalbe sewantly woven throughout. 1865 JENNINGS Obs. Dial. W. Eng. 73 Suently, evenly, smoothly, plainly.