How have courts considered the meaning of the word "willful" in relation to income tax evasion?

In Spies v. United States (1943) 317 U.S. 492, 63 S.Ct. 364, 87 L.Ed. 418, the court considered a statute that made it a felony for a person who " 'willfully attempts in any manner to evade or defeat any tax imposed by' " specified provisions. (Id. at p. 494, fn. 2, 63 S.Ct. 364.) This was in contrast to a misdemeanor statute that punished simply the "willful failure to pay" income tax or supply the proper information. (Id. at p. 493, 63 S.Ct. 364.) The court again acknowledged that "willful ... is a word of many meanings, its construction often being influenced by context." (Id. at p. 497, 63 S.Ct. 364.) The court derived the differing meanings of "willful" in the two statutes not so much from the word itself, but from the "attempt to evade" language in the felony statute. (Id. at pp. 498-499, 63 S.Ct. 364.) Contrasting the felony and misdemeanor statutes, the court stated: "Willful but passive neglect of the statutory duty may constitute the lesser offense, but to combine with it a willful and positive attempt to evade tax in any manner or to defeat it by any means lifts the offense to the degree of felony." (Id. at p. 499, 63 S.Ct. 364.)