The Collaborative International Dictionary of English v.0.48:

Lengthy \Length"y\ (-[y^]), a. [Compar. Lengthier
   (-[i^]*[~e]r); superl. Lengthiest.]
   Having length; rather long or too long; prolix; not brief; --
   said chiefly of discourses, writings, and the like. "Lengthy
   periods." --Washington. "Some lengthy additions." --Byron.
   "These would be details too lengthy." --Jefferson. "To cut
   short lengthy explanations." --Trench.
   [1913 Webster] Lenience