The Collaborative International Dictionary of English v.0.48:
Blanket stitch \Blanket stitch\ A buttonhole stitch worked wide apart on the edge of material, as blankets, too thick to hem. [Webster 1913 Suppl.]WordNet (r) 3.0 (2006):
blanket stitch n 1: a strong reinforcing stitch for edges of blanket and other thick material; similar to buttonhole stitch