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Webster 1913 Edition

Adj.

Having no curb or restraint.

curbless ‎(comparative more curbless, superlative most curbless)

Without restraint; uncurbed, unchecked.
- 1856, Jared Sparks, Edward Everett, James Russell Lowell, Henry Cabot Lodge, The North American Review‎
  His force was the preternatural activity of a strong imagination, which, curbless and uncontrolled, bore him whithersoever it would.
Without a curb (raised margin).
- 2008, Wendy A Jordan, Universal Design for the Home
  Both the long, angled wall and another, shorter wall in the curbless shower contain glass block windows that provide natural light...