breadthen,v.|ˈbrɛdθən| [f.prec.: after lengthen.] intr. To increase in breadth; to broaden, widen. 1809W. Taylor in Robberds Mem. II. 278 The inroads of mediocrity are ever breadthening.1884A. Forbes in Eng.Illustr.Mag. Apr. 455/2 As I painted, the picture breadthened on the canvas.